TF-A GICv3 driver: Change API for GICR_IPRIORITYR accessors

To support compatibility with previous GICv3 driver version
this patch:
- restores original API for gicr_read_ipriority() and
gicr_wrtite_ipriority() functions;
- adds accessor functions for GICR_XXX0,1 registers, e.g.
GICR_IGROUPR0, GICR_ICFGR0, GICR_ICFGR1, etc.

Change-Id: I796a312a61665ff384e3d9de2f4b3c60f700b43b
Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
diff --git a/drivers/arm/gic/v3/gicrv3_helpers.c b/drivers/arm/gic/v3/gicrv3_helpers.c
index e46b15e..3004054 100644
--- a/drivers/arm/gic/v3/gicrv3_helpers.c
+++ b/drivers/arm/gic/v3/gicrv3_helpers.c
@@ -18,6 +18,20 @@
  ******************************************************************************/
 
 /*
+ * Accessors to read/write the GIC Redistributor IPRIORITYR and IPRIORITYRE
+ * register corresponding to the interrupt `id`, 4 interrupts IDs at a time.
+ */
+unsigned int gicr_read_ipriorityr(uintptr_t base, unsigned int id)
+{
+	return GICR_READ(IPRIORITY, base, id);
+}
+
+void gicr_write_ipriorityr(uintptr_t base, unsigned int id, unsigned int val)
+{
+	GICR_WRITE(IPRIORITY, base, id, val);
+}
+
+/*
  * Accessor to set the byte corresponding to interrupt `id`
  * in GIC Redistributor IPRIORITYR and IPRIORITYRE.
  */