tpm: fix tpm_acpi sparse warning on different address spaces

acpi_os_map_memory expects its return value to be in the __iomem address
space. Tag the variable we're using as such and use memcpy_fromio to
avoid further sparse warnings.

Signed-off-by: Kent Yoder <key@linux.vnet.ibm.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>