target/i386: change X86_ENTRYwr to use T0, use it for moves

target/i386: change X86_ENTRYwr to use T0, use it for moves

Just like X86_ENTRYr, X86_ENTRYwr is easily changed to use only T0.
In this case, the motivation is to use it for the MOV instruction
family.  The case when you need to preserve the input value is the
odd one, as it is used basically only for BLS* instructions.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>