[CompilerRT] use .p2align, .balign instead of .align

The .align statements in ARM assembly routines is actually meant to be a power
of 2 alignment (e.g. .align 2 == 4 byte alignment, not 2).  Switch to using
.p2align.  .p2align is guaranteed to be a power-of-two alignment always and much
more explicit.

The .align in the case of x86_64 is byte alignment, use .balign instead of
.align.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@208578 91177308-0d34-0410-b5e6-96231b3b80d8