ppc/xive: Add xive_tctx_pipr_present() to present new interrupt

ppc/xive: Add xive_tctx_pipr_present() to present new interrupt

xive_tctx_pipr_update() is used for multiple things. In an effort
to make things simpler and less overloaded, split out the function
that is used to present a new interrupt to the tctx.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
Reviewed-by: Michael Kowal <kowal@linux.ibm.com>
Tested-by: Gautam Menghani <gautam@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20250512031100.439842-31-npiggin@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>