RISC-V: PR25212, Report errors for invalid march and mabi combinations.

RISC-V: PR25212, Report errors for invalid march and mabi combinations.

This patch clarify the following invalid combinations of march and mabi,
* ilp32f/lp64f abi without f extension.
* ilp32d/lp64d abi without d extension.
* ilp32q/lp64q abi without q extension.
* e extension with any abi except ilp32e

GNU assembler reports errors when finding the above invalid combinations.
But LLVM-MC reports warnings and ignores these invalid cases.  It help to
set the correct ilp32/lp64/ilp32e abi according to rv32/rv64/rve.  This
looks good and convenient, so perhaps we can do the same things.  However,
if you don't set the mabi, GNU assembler also try to set the suitable
ABI according to march/elf-attribute.  Compared to LLVM-MC, we will choose
double/quad abi if d/f extension is set.

gas/
    PR 25212
    * config/tc-riscv.c (riscv_set_abi_by_arch): If -mabi isn't set, we
    will choose ilp32e abi for rv32e.  Besides, report errors for the
    invalid march and mabi combinations.
    * testsuite/gas/riscv/mabi-attr-rv32e.s: New testcase.  Only accept
    ilp32e abi for rve extension.
    * testsuite/gas/riscv/mabi-fail-rv32e-lp64f.d: Likewise.
    * testsuite/gas/riscv/mabi-fail-rv32e-lp64f.l: Likewise.
    * testsuite/gas/riscv/mabi-fail-rv32e-lp64d.d: Likewise.
    * testsuite/gas/riscv/mabi-fail-rv32e-lp64d.l: Likewise.
    * testsuite/gas/riscv/mabi-fail-rv32e-lp64d.q: Likewise.
    * testsuite/gas/riscv/mabi-fail-rv32e-lp64d.q: Likewise.
    Renamed all mabi testcases to their march-mabi settings.