Create common files for ARM32 and ARM64 common code

Create common files for ARM32 and ARM64 common code

Create codegenarmarch.cpp, lowerarmarch.cpp, lsraarmarch.cpp.

For codegenarmarch.cpp, I copied over a bunch of functions that
are almost identical between arm and arm64. I left the functions
intact (didn't change anything), so created one for ARM32 and
one for ARM64, unless they were truly identical. A follow-up
will be to actually merge the functions.

For lowerarmarch.cpp and lsraarmarch.cpp, I did the function
merge for nearly (or completely) identical functions, since
there were so many that were so similar.