target-i386: Tidy extend + move

target-i386: Tidy extend + move

For the known MO_32/MO_64 cases, we don't need to extend a 32-bit temp
into a 64-bit temp before storing into the hardware register.

We do need the extension for the MO_8/MO_16 cases, in order for the
deposit_tl operation to work, so leave those alone.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>