tls: pstm code shrink

tls: pstm code shrink

Optimize ABI calling convention and "dead code" cases where return value
is known to be always "success".

function                                             old     new   delta
pstm_mod                                             113    1227   +1114
pstm_exptmod                                        1463    1532     +69
pstm_montgomery_reduce                               381     393     +12
pstm_sqr_comba                                       478     487      +9
pstm_mul_comba                                       447     452      +5
der_binary_to_pstm                                    42      45      +3
pstm_count_bits                                       48      46      -2
pstm_clear                                            72      70      -2
pstm_clamp                                            57      55      -2
pstm_zero                                             38      34      -4
pstm_init_size                                        46      42      -4
pstm_init_for_read_unsigned_bin                       24      20      -4
pstm_grow                                             72      68      -4
pstm_unsigned_bin_size                                37      32      -5
pstm_cmp_mag                                          78      72      -6
pstm_copy                                             92      84      -8
pstm_mul_d                                           224     215      -9
pstm_rshd                                            104      94     -10
pstm_mul_2                                           156     146     -10
tls_handshake                                       2085    2072     -13
psRsaEncryptPub                                      421     408     -13
pstm_lshd                                            109      95     -14
pstm_cmp                                              54      39     -15
s_pstm_sub                                           228     212     -16
pstm_init_copy                                        72      52     -20
pstm_read_unsigned_bin                               109      88     -21
pstm_mulmod                                          120      99     -21
s_pstm_add                                           337     314     -23
pstm_add                                             108      84     -24
pstm_mul_2d                                          186     161     -25
pstm_sub                                             102      74     -28
pstm_to_unsigned_bin                                 151     120     -31
pstm_set                                              34       -     -34
pstm_div_2d                                          409     373     -36
pstm_init                                             42       -     -42
pstm_exch                                             50       -     -50
pstm_montgomery_setup                                 89       -     -89
pstm_2expt                                            96       -     -96
pstm_montgomery_calc_normalization                   140       -    -140
pstm_div                                            1522       -   -1522
------------------------------------------------------------------------------
(add/remove: 0/7 grow/shrink: 6/27 up/down: 1212/-2343)     Total: -1131 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>