[POWERPC] 8xx: Move softemu8xx.c from arch/ppc

[POWERPC] 8xx: Move softemu8xx.c from arch/ppc

Previously, Soft_emulate_8xx was called with no implementation, resulting in
build failures whenever building 8xx without math emulation.  The
implementation is copied from arch/ppc to resolve this issue.

However, this sort of minimal emulation is not a very good idea other than
for compatibility with existing userspaces, as it's less efficient than
soft-float and can mislead users into believing they have soft-float.  Thus,
it is made a configurable option, off by default.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>