m68k: Rework asm/global_data.h slightly

In the architecture global data, replace the one case of u32 with
unsigned long. Now, we can drop config.h here but then do need to add it
in two m68k-centric spaces.

Acked-by: Angelo Dureghello <angelo@kernel-space.org>
Signed-off-by: Tom Rini <trini@konsulko.com>