[AArch64][AsmParser] NFC: Cleanup of addOperands functions

Most of the add<operandname>Operands() functions are the same
and can be replaced by using a single 'RenderMethod' in
the AArch64InstrFormats.td file. Since many of the scaled
immediates (with different scaling/bits) are the same, most of
these can reuse the same AsmOperandClass.

Reviewers: fhahn, rengolin, samparker, SjoerdMeijer, javed.absar

Reviewed By: samparker

Differential Revision: https://reviews.llvm.org/D46122

llvm-svn: 331146