m68k: code reformatting for all start.S files

This patch is style-related only, to reformat all the start.S code,
actually not following a coherent style inside single files and
between different cpu start.S files.

Linux format has been respected, as
  - max line width at 80 columns
  - one 8 cols tab between asm instructions and operands
  - inline comments, where any, fixed at col 41

Signed-off-by: Angelo Dureghello <angelo@sysam.it>