powerpc: Make STRICT_MM_TYPECHECKS a config option

The STRICT_MM_TYPECHECKS code has bit-rotted over the years. To make it
possible to easily build test it, make it a CONFIG option.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --cc arch/powerpc/Kconfig.debug
Simple merge

diff --cc arch/powerpc/include/asm/page.h
Simple merge

diff --cc arch/powerpc/include/asm/pgtable-ppc64.h
Simple merge