Try to implement the handling of MOVD as attempted in checkin:
70712c0df6c437c50452c4997aa2e3de5a0e0299
and reverted in:
d279fbbd80aab6f79584249629a4aea90b851458
due to BR3392199. This time make sure to use the SX flag to only
match when a size is explicitly given, and also don't duplicate the 0F
6F/7F opcodes, which are documented as MOVQ by AMD as well as Intel.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
