m68k/UAPI: Move generic definitions to <asm/bootinfo.h>

Move generic definitions used by bootstraps to uapi/asm/bootinfo.h:
  - Machine types,
  - CPU, FPU, and MMU types,
  - struct mem_info.

Keep a copy of struct mem_info for in-kernel use, and rename it to struct
m68k_mem_info, as the exported one will be modified later.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>