This reverts commit 6ac9b617.

This commit was required because at that time, ioread/iowrite
functions were sub-optimal on powerpc/32 compared to the
architecture specific in_/out_ IO accessors.

But there are now equivalent since
commit 894fa235 ("powerpc: inline iomap accessors").
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Li Yang <leoyang.li@nxp.com>