m68k: make fp register stores consistent for m68k and ColdFire

There is no reason we can't make the saved fp registers the same for all
m68k types and ColdFire. There is a little wasted space, but the code
consistency and cleanliness is a big win.

sigcontext.h is an exported header, but currently there is no in-mainline
users of the !__uClinux__ and __mcoldfire__ case that this change effects.
Even better this change actually makes this structure consistent with
the out-of-mainline ColdFire/MMU code.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>