[RISCV] Allow llvm-objdump to disassemble objects with unrecognised versions of known extensions

This Moves ELFObjectFile to using
RISCVISAInfo::parseNormalizedArchString which is not an NFC, as the test
changes show. D144353 transitioned LLD to using this function, which is
specialised to parsing arch strings in the normalised format specified
in the psABI rather than user-authored strings accepted in `-march`,
which has greater flexibility.

parseNormalizedArchString does not ignore or produce an error for ISA
extensions with a version that isn't recognised/supported by LLVM. As
current GCC is marking its objects with a higher version of the A, F,
and D extensions than LLVM (see [extension versioning
discussion](https://discourse.llvm.org/t/rfc-resolving-issues-related-to-extension-versioning-in-risc-v/68472)
this massively improves the usability of llvm-objdump with such
binaries.

Differential Revision: https://reviews.llvm.org/D146114