S12Z: Add alias instructions BHS and BLO.

These are documented by NXP as alternative mnemonics for BCC and BCS
respectively.

gas/ChangeLog:

        * config/tc-s12z.c (opcodes): bhs, blo: New members.
	* testsuite/gas/s12z/bra.d: Add tests for aliases.
	* testsuite/gas/s12z/bra.s: Add tests for aliases.