powerpc: add 2 common dcache assembly functions

This patch defines the 2 flush_dcache_range and invalidate_dcache_range
functions for all the powerpc architecture. Their implementation is
borrowed from the kernel's misc_32.S file and replace the ones from
mpc86xx and ppc4xx since they were equivalent.

This is a fix for the problem introduced by this patch:
http://patchwork.ozlabs.org/patch/448849/



Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: York Sun <yorksun@freescale.com>