ArmPkg: Adjust variable type and cast for RegShift & RegOffset

According to the GIC architecture version 3 and 4 specification, the
maximum number of INTID bits supported in the CPU interface is 24.

Considering this the RegShift variable is not required to be more than 8
bits. Therefore, make the RegShift variable type to UINT8.  Also add
necessary typecasts when calculating the RegOffset and RegShift values.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>

ArmPkg/Drivers/ArmGic/GicV2/ArmGicV2Dxe.c

@@ -393,7 +393,7 @@ GicV2DxeInitialize (
   EFI_STATUS  Status;
   UINTN       Index;
   UINT32      RegOffset;
-  UINTN       RegShift;
+  UINT8       RegShift;
   UINT32      CpuTarget;
 
   // Make sure the Interrupt Controller Protocol is not already installed in
@@ -411,8 +411,8 @@ GicV2DxeInitialize (
     GicV2DisableInterruptSource (&gHardwareInterruptV2Protocol, Index);
 
     // Set Priority
-    RegOffset = Index / 4;
-    RegShift  = (Index % 4) * 8;
+    RegOffset = (UINT32)(Index / 4);
+    RegShift  = (UINT8)((Index % 4) * 8);
     MmioAndThenOr32 (
       mGicDistributorBase + ARM_GIC_ICDIPR + (4 * RegOffset),
       ~(0xff << RegShift),