pnv/xive2: VC_ENDC_WATCH_SPEC regs should read back WATCH_FULL

pnv/xive2: VC_ENDC_WATCH_SPEC regs should read back WATCH_FULL

Firmware expects to read back the WATCH_FULL bit from the VC_ENDC_WATCH_SPEC
register, so don't clear it on read.

Don't bother clearing the reads-as-zero CONFLICT bit because it's masked
at write already.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
Reviewed-by: Michael Kowal <kowal@linux.ibm.com>
Reviewed-by: Caleb Schlossin <calebs@linux.ibm.com>
Tested-by: Gautam Menghani <gautam@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20250512031100.439842-20-npiggin@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>