nasm: movhps compatibility QWORD->MMWORD

Filed for nasm as:
https://sourceforge.net/tracker/?func=detail&atid=106208&aid=3081103&group_id=6208

nasm just does not accept any size parameter for movhps:
1.asm:2: error: mismatch in operand sizes

Some parts of libvpx already use MMWORD for movhps and MMWORD is
defined-out so it is compatible both with yasm and nasm.

Provide nasm compatibility. No binary change by this patch with yasm on
{x86_64,i686}-fedora13-linux-gnu.

Change-Id: I4008a317ca87ec07c9ada958fcdc10a0cb589bbc