x86: Cleanup register operand decoding
x86: Cleanup register operand decoding

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@cs.helsinki.fi>

ukatemi/libcpu,libcpu/libcpu,glguida/libcpu,libcpu/libcpu,ukatemi/libcpu,curtiszimmerman/libcpu,curtiszimmerman/libcpu,glguida/libcpu,ukatemi/libcpu,libcpu/libcpu,curtiszimmerman/libcpu,glguida/libcpu,monocasa/libcpu,glguida/libcpu,ukatemi/libcpu,monocasa/libcpu,curtiszimmerman/libcpu,monocasa/libcpu,libcpu/libcpu,monocasa/libcpu