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.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