m68k: merge mmu and non-mmu versions of asm-offsets.c

It is strait forward to merge the mmu and non-mmu versions of
asm-offstes.c. Some name changes are required for the preempt and
thread_info.flags in the non-mmu entry.S assembler to make them
consistent for both setups.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>