s390: Support CONFIG_TRACE_MMIO_ACCESS

Enable the functionality of commits
d593d64f ("lib: Add register read/write tracing support")
21003197 ("asm-generic/io: Add logging support for MMIO accessors").

It only depends on explicit function calls for the tracing.

Signed-off-by: Steffen Maier <maier@linux.ibm.com>
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>