[AArch64] Prefer "mov" over "orr" to materialize constants.

This is generally more readable due to the way the assembler aliases
work.

(This causes a lot of test changes, but it's not really as scary as it
looks at first glance; it's just mechanically changing a bunch of checks
for orr to check for mov instead.)

Differential Revision: https://reviews.llvm.org/D59720

llvm-svn: 356954