MIPS/GAS/testsuite: Implement individual MIPS16 ISA testing

MIPS/GAS/testsuite: Implement individual MIPS16 ISA testing

Implement individual MIPS16 ISA GAS testing for the 32-bit and 64-bit
variants of the base MIPS16 and the MIPS16e ISA each.

	gas/
	* testsuite/gas/mips/mips.exp (run_dump_test_arch): Add
	`mips16e' and `mips16' prefixes.
	(run_list_test_arch): Likewise.
	Rename `mips16' architecture to `mips16-32'.  Add `mips16-64',
	`mips16e-32' and `mips16e-64' architectures.  Update `rol64',
	`mips16e', `elf${el}-rel2' and `elf-rel4' test invocations
	accordingly.
	* testsuite/gas/mips/mips16e@branch-swap-3.d: New test.
	* testsuite/gas/mips/mips16e@branch-swap-4.d: New test.
	* testsuite/gas/mips/mips16e@loc-swap-dis.d: New test.
	* testsuite/gas/mips/mips16e@loc-swap.d: New test.