Fix assembler warnings.

There are a few instructions deprecated on armv8 that result in lots
of warnings. Add an arch directive so that these warnings go away.

This doesn't cause any problems because the instructions still
execute properly.

Bug: 38319728

Test: Built all of these assembler files and verified the warning are gone.
Change-Id: If063defdd16f290c01975233c8d257d1b2005e76