RISC-V: Remove RV32EF conflict

RISC-V: Remove RV32EF conflict

Despite that the RISC-V ISA Manual version 2.2 prohibited "RV32EF", later
versions beginning with the version 20190608-Base-Ratified removed this
restriction.  Because the 'E' extension is still a draft, the author chose
to *just* remove the conflict (not checking the ISA version).

Note that, because RV32E is only used with a soft-float calling convention,
there's no valid official ABI for RV32EF.  It means, even if we can assemble
a program with -march=rv32ef -mabi=ilp32e, floating-point registers are kept
in an unmanaged state (outside ABI management).

The purpose of this commit is to suppress unnecessary errors while parsing
an ISA string and/or disassembling, not to allow hard-float with RVE.

bfd/ChangeLog:

	* elfxx-riscv.c (riscv_parse_check_conflicts): Accept RV32EF
	because only older specifications disallowed it.

gas/ChangeLog:

	* testsuite/gas/riscv/march-fail-rv32ef.d: Remove as not directly
	prohibited.
	* testsuite/gas/riscv/march-fail-rv32ef.l: Likewise.