fbsplash: shrink, better help text; inifile cannot specify image now;

fbsplash: shrink, better help text; inifile cannot specify image now;
image can come from stdin

function                                             old     new   delta
packed_usage                                       23872   23932     +60
static.param_names                                     -      57     +57
fbsplash_main                                       1525    1472     -53
static.param_value                                   100       -    -100
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 1/1 up/down: 117/-153)          Total: -36 bytes
   text    data     bss     dec     hex filename
 801202     641    7380  809223   c5907 busybox_old
 801181     641    7380  809202   c58f2 busybox_unstripped