i3c: mipi-i3c-hci: Cache DAT in memory for Runtime PM restore

i3c: mipi-i3c-hci: Cache DAT in memory for Runtime PM restore

Prepare for Runtime PM support, which requires restoring the Device Address
Table (DAT) registers after resume.  Maintain a copy of DAT in memory so it
can be reprogrammed when the controller is powered back up.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260113072702.16268-9-adrian.hunter@intel.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>