arch,cpu: Rename RegClass to RegClassType.

This type is really an index which selects a RegClass, not a RegClass
itself.

A follow on change will rename RegClassInfo to RegClass.

Change-Id: I2c1b1d4105bd11b58680053b484d4c1aa1055a9f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/45229
Maintainer: Gabe Black <gabe.black@gmail.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/arm/tracers/tarmac_record.hh

@@ -162,7 +162,7 @@ class TarmacTracerRecord : public TarmacBaseRecord
         /** True if register entry is valid */
         bool regValid;
         /** Register class */
-        RegClass regClass;
+        RegClassType regClass;
         /** Register arch number */
         RegIndex regRel;
         /** Register name to be printed */