[Bultin][ARM] Make aeabi_memset be Thumb1 compatible and other asm

syntax fix

Summary:
Make the asm of  aeabi_memset be assembled for thumb1.
Also fix some instructions to conform with the syntax of ARM reference manual.
For example, muls requires the form of "Rd, Rn, Rd" and orrs requires
the form of "Rd, Rm". Clang-as is benign but it may fail other assembler
if not in the exact form.

Reviewers: rengolin, compnerd, kubamracek

Reviewed By: rengolin, compnerd

Subscribers: aemerson, llvm-commits, mgorny

Differential Revision: https://reviews.llvm.org/D28971

llvm-svn: 292727