media: fsl-viu: Use the ioread/write32be() accessors

Since commit 29d75068 ("media: fsl-viu: allow building it with
COMPILE_TEST") there were several attempts to fix build failures on
PPC, MICROBLAZE and M68K.

However, such errors are still present as reported by kbuild robot.

Fix the problem by using the ioread/write32be() accessors, which build
fine on all platforms.

Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>