arm: Get rid of some register type definitions.

arm: Get rid of some register type definitions.

These are IntReg, FloatReg, FloatRegBits, and MiscReg. These have been
supplanted by the global types RegVal and FloatRegVal.

Change-Id: Ief1cd85d0eff7156282ddb1ce168a2a5677f7435
Reviewed-on: https://gem5-review.googlesource.com/c/13625
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>