[PATCH v2] RISC-V: Accept version, supervisor extension and more than one NSE for -march.

[Kito Cheng]

Hi Jim:

I've addressed most issues in you mail exclude newer spec update like
Z* and RV32E with F/D :)

Tested on CentOS 7 (GCC 4.8.5).

Changes since v1:
- Fixed several typos.
- Minor variable naming fixes (ext -> subset, subset to subset_list).
- Remove riscv_next_arch_char.
- Refine riscv_parsing_subset_version, remove last one argument, spec
only allow underscore between each ISA subset components[1].
- Add comment to explain argument and return value for
riscv_parsing_subset_version, riscv_parse_std_ext,
riscv_parse_sv_or_non_std_ext and riscv_parse_subset.
- Fix ChangeLog.
- Fix build error.
- Fix opcodes/riscv-dis.c.
- Two more testcase march-ok-g2_p1.d and march-ok-i2p0m2_a2f2.d

[1] https://github.com/riscv/riscv-isa-manual/commit/87d431236b5a01ff80e3567e602fdeaa797e97e8

[Jim Wilson]

Post by Kito Cheng
I've addressed most issues in you mail exclude newer spec update like
Z* and RV32E with F/D :)

Thanks. This looks OK to me. I committed it with some minor
ChangeLog entry edits.

Jim