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/ArmLibSupportV7.S

@@ -60,6 +60,10 @@ ASM_FUNC(ArmDisableInterrupts)
   isb
   bx      LR
 
+ASM_FUNC(ArmReadIdMmfr4)
+  mrc    p15,0,r0,c0,c2,6     @ Read ID_MMFR4 Register
+  bx     lr
+
 // UINT32
 // ReadCCSIDR (
 //   IN UINT32 CSSELR

ArmPkg/Library/ArmLib/Arm/ArmLibSupportV7.asm

@@ -64,6 +64,10 @@
   isb
   bx      LR
 
+ RVCT_ASM_EXPORT ArmReadIdMmfr4
+  mrc    p15,0,r0,c0,c2,6     ; Read ID_MMFR4 Register
+  bx     LR
+
 // UINT32
 // ReadCCSIDR (
 //   IN UINT32 CSSELR

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
   );