fdisk: many significant improvements and fixes to Sun label handling

fdisk: many significant improvements and fixes to Sun label handling

1) Properly describe the exact layout and fields of the sun disk
   label.  Several fields were incorrectly mentioned and others
   wrongly sized.

2) Properly set the version, sane, and num_partitions fields.

   Because we weren't doing this, programs such as Solaris's format
   and the Solaris kernel itself refused to recognize our disk labels
   as valid.

3) Move SSWAP*() macros into fdisksunlabel.c as there is no reason
   for them to be exposed to the rest of fdisk.

4) Kill the sun_predefined_drives array hack and assosciated code.

   Instead size the disk and figure out the geometry properly just
   like the SGI and MSDOS partition handling do, by means of the
   HD_GETGEO ioctl() and disksize().

5) If the disk label read is found to not have the proper values
   set in version, sane, or num_partitions, fix them, recompute the
   label checksum, dirty the disk label, and let the user know what
   we did and that the fixed values will be written out if they 'w'.

   This gives users an easy way to fix up disk labels created by
   disk labelling programs which had this bug.

6) Create a sun_sys_getid() function so that fdisk.c does not need
   to reference the sun disk label details directly, just like the
   SGI code does.

Signed-off-by: David S. Miller <davem@davemloft.net>