ppc/pnv: Add OCC FLAG registers

OCCFLG are scratch registers that can be shared with OCC firmware.
Log reads and writes to the registers as a reminder when we run
into more OCC code.

Add RW, WO_CLEAR and WO_OR SCOM Type enums in pnv_occ.c

Reviewed-by: Chalapathi V <chalapathi.v@linux.ibm.com>
Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
Reviewed-by: Aditya Gupta <adityag@linux.ibm.com>
Signed-off-by: Chalapathi V <chalapathi.v@linux.ibm.com>
Signed-off-by: Caleb Schlossin <calebs@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20260210134647.2050821-4-calebs@linux.ibm.com
Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>