Get rid of the WANT_COMPAT_REG_H test and instead define both the 32-
and 64-bit register offset definitions at the same time with
MIPS{32,64}_ prefixes, then define the existing EF_* names to the
correct definitions for the kernel's bitness.

This patch is a prerequisite of the following bug fix patch.
Signed-off-by: NAlex Smith <alex@alex-smith.me.uk>
Cc: <stable@vger.kernel.org> # v3.13+
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7451/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>