powerpc: Remove unused devm_ioremap_prot()

Added in 2008, but has never had any in-tree users, and no other
architectures provide it.

Signed-off-by: Kyle McMartin <kyle@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

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

diff --cc arch/powerpc/lib/Makefile
Simple merge

diff --cc arch/powerpc/lib/devres.c
Simple merge