Added another bit of the ARM target assembler to llvm-mc to parse register

lists.  Changed ARMAsmParser::MatchRegisterName to return -1 instead of 0 on
errors so 0-15 values could be returned as register numbers.  Also added the
rest of the arm register names to the currently hacked up version to allow more
testing.  Some changes to ARMAsmParser::ParseOperand to give different errors
for things not yet supported and some additions to the hacked
ARMAsmParser::MatchInstruction to allow more testing for now.

llvm-svn: 83673