Remove stack shadowing for x86-x64 for SAD functions.

x86-64 passes arguments in registers.  There is no need to push
them to the stack before using them.

This fixes 15acc84f10cefd98b2f8dbd2eac2cc92c5a3f851 where ebx
was not getting preserved on x86.

Change-Id: I1214b5f818a0201f75ab6ad7d5c6f448e09b16c2
1 file changed