hw/intc/arm_gicv3: Add cast to match the documentation

The result of 1 << regbit with regbit==31 has a 1 in the 32nd bit.
When cast to uint64_t (for further bitwise OR), the 32 most
significant bits will be filled with 1s. However, the documentation
states that the upper 32 bits of ICC_AP[0/1]R<n>_EL2 are reserved.

Add an explicit cast to match the documentation.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Cc: [email protected]
Fixes: 28cca59 ("hw/intc/arm_gicv3: Add NMI handling CPU interface registers")
Signed-off-by: Alexandra Diupina <[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>
(cherry picked from commit 12dc8f6)
Signed-off-by: Michael Tokarev <[email protected]>

hw/intc/arm_gicv3_cpuif.c

@@ -1170,7 +1170,7 @@ static void icc_activate_irq(GICv3CPUState *cs, int irq)
     if (nmi) {
         cs->icc_apr[cs->hppi.grp][regno] |= ICC_AP1R_EL1_NMI;
     } else {
-        cs->icc_apr[cs->hppi.grp][regno] |= (1 << regbit);
+        cs->icc_apr[cs->hppi.grp][regno] |= (1U << regbit);
     }
 
     if (irq < GIC_INTERNAL) {