powerpc32: refactor x_mapped_by_bats() and x_mapped_by_tlbcam() together

x_mapped_by_bats() and x_mapped_by_tlbcam() serve the same kind of
purpose, and are never defined at the same time.
So rename them x_block_mapped() and define them in the relevant
places

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <oss@buserror.net>