arch-power: Add fields for D and X form instructions

This adds the L field for D and X form instructions that
specifies if a compare instruction should perform 32-bit
or 64-bit comparison of its operands.

Change-Id: I72413a507c93096b1573836197837227c1c1e521
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40911
Reviewed-by: Boris Shingarov <shingarov@labware.com>
Maintainer: Boris Shingarov <shingarov@labware.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/power/types.hh

@@ -59,6 +59,9 @@ BitUnion32(ExtMachInst)
     Bitfield<20, 16> d1;
     Bitfield< 1,  0> d2;
 
+    // Compare fields
+    Bitfield<21>     l;
+
     // Special purpose register identifier
     Bitfield<20, 11> spr;
     Bitfield<25, 23> bf;