MIPS/GAS/testsuite: Run RFE test across all ISAs

Verify that the RFE instruction is not only accepted where supported,
but rejected where it is not as well.

	gas/
	* testsuite/gas/mips/mips.exp: Run RFE test across all ISAs.
	* testsuite/gas/mips/rfe.d: Update for ISA exclusions.
	* testsuite/gas/mips/mips1@rfe.d: New test.
	* testsuite/gas/mips/mips2@rfe.d: New test.
	* testsuite/gas/mips/r3000@rfe.d: New test.
	* testsuite/gas/mips/r3900@rfe.d: New test.
	* testsuite/gas/mips/rfe.l: New test stderr output.