Register names are capitalized.
using is more common in newer code. This doesn't have to copy from other targets.
Patch is updated according to latest upstream version. Updated licenses.
Patch is updated according to LLVM upstream version and latest Xtensa backend version.
Correct instruction descriptions, format descriptions and instruction operands according to common style for *.td files. The llvm_unreachable is substituted to report_fatal_error.