x86emul: use unambiguous register names

x86emul: use unambiguous register names

This is in preparation of eliminating the mis-naming of 64-bit fields
with 32-bit register names (eflags instead of rflags etc).

Note that the result is not fully consistent until after at least one
more patch is in place, primarily to limit patch size (by trying to not
touch the same line twice).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>