ArmPkg: Add helper function to read the Memory Model Feature Register 4

In AARCH32, CCIDX support is indicated in the MMFR4 register - unlike
under AARCH64 where it's in MMFR2. Add a helper function to read it.

Signed-off-by: Rebecca Cran <rebecca@nuviainc.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>

ArmPkg/Library/ArmLib/Arm/ArmV7Lib.h

@@ -48,9 +48,13 @@ ArmCleanInvalidateDataCacheEntryBySetWay (
   IN  UINTN   SetWayFormat
   );
 
-UINTN
+/** Reads the ID_MMFR4 register.
+
+   @return The contents of the ID_MMFR4 register.
+**/
+UINT32
 EFIAPI
-ArmReadIdPfr0 (
+ArmReadIdMmfr4 (
   VOID
   );