MIPS16/opcodes: Use hexadecimal interpretation for the `e' operand code

MIPS16/opcodes: Use hexadecimal interpretation for the `e' operand code

Make the `e' operand code used with raw EXTEND instructions use the
hexadecimal rather than decimal format, for consistency with what is
actually produced by code in `print_insn_mips16' dedicated to EXTEND
disassembly.  Due to that special handling the operand code is only
interpreted for assembly however, which accepts either format either
way, so there is no functional change here.

	opcodes/
	* mips16-opc.c (decode_mips16_operand) <'e'>: Use HINT rather
	than UINT.

	gas/
	* testsuite/gas/mips/mips16-extend.d: New test.
	* testsuite/gas/mips/mips16-extend.s: New test source.
	* testsuite/gas/mips/mips.exp: Run the new test.