fdisk: move more data to struct globals; shrink code

fdisk: move more data to struct globals; shrink code

function                                             old     new   delta
nowarn                                                 1       -      -1
listing                                                1       -      -1
dos_compatible_flag                                    1       -      -1
warn_cylinders                                        44      42      -2
open_list_and_close                                  364     362      -2
fdisk_fatal                                           41      38      -3
verify                                              1053    1049      -4
user_sectors                                           4       -      -4
user_heads                                             4       -      -4
user_cylinders                                         4       -      -4
pt_sectors                                             4       -      -4
pt_heads                                               4       -      -4
kern_sectors                                           4       -      -4
kern_heads                                             4       -      -4
ext_index                                              4       -      -4
total_number_of_sectors                                8       -      -8
extended_offset                                        8       -      -8
create_doslabel                                      129     120      -9
write_table                                          225     211     -14
delete_partition                                     445     431     -14
set_partition                                        476     459     -17
list_disk_geometry                                   247     229     -18
unable_to_write                                       19       -     -19
add_partition                                       2515    2486     -29
get_boot                                            1709    1636     -73
fdisk_main                                          2812    2679    -133
------------------------------------------------------------------------------
(add/remove: 0/14 grow/shrink: 0/12 up/down: 0/-388)         Total: -388 bytes
   text    data     bss     dec     hex filename
 804634     611    6852  812097   c6441 busybox_old
 804298     610    6804  811712   c62c0 busybox_unstripped