Add a new function specifically for mapping the register blocks and
offsets within. The new function can be used more generically for other
register block identifiers.

No functional change is meant to be introduced in this patch with the
exception of a dev_err printed when the device register block isn't
found.
Signed-off-by: NBen Widawsky <ben.widawsky@intel.com>
Reviewed-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20210407222625.320177-3-ben.widawsky@intel.comSigned-off-by: NDan Williams <dan.j.williams@intel.com>