irqchip/gic-v4.1: Fix programming of GICR_VPROPBASER_4_1_SIZE

The Size field of GICv4.1 VPROPBASER register indicates number of
pages minus one and together Page_Size and Size control the vPEID
width. Let's respect this requirement of the architecture.
Signed-off-by: NZenghui Yu <yuzenghui@huawei.com>
Signed-off-by: NMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200206075711.1275-2-yuzenghui@huawei.com

drivers/irqchip/irq-gic-v3-its.c

@@ -2531,7 +2531,7 @@ static int allocate_vpe_l1_table(void)
 		npg = 1;
 	}
 
-	val |= FIELD_PREP(GICR_VPROPBASER_4_1_SIZE, npg);
+	val |= FIELD_PREP(GICR_VPROPBASER_4_1_SIZE, npg - 1);
 
 	/* Right, that's the number of CPU pages we need for L1 */
 	np = DIV_ROUND_UP(npg * psz, PAGE_SIZE);