S12Z: GAS: Allow #_symbol operands as mov source

S12Z: GAS: Allow #_symbol operands as mov source

mov.l, mov.p and mov.w (but not mov.b) when called with an immediate source
operand should be accepted a relocatable expression.  This change makes that
possible.

gas/
	* config/tc-s12z.c (lex_imm): Add new argument exp_o.
	(emit_reloc): New function.
	(md_apply_fix): [BFD_RELOC_S12Z_OPR] Recognise that it
	can be either 2 bytes or 3 bytes long.
	* testsuite/gas/s12z/mov-imm-reloc.d: New file.
	* testsuite/gas/s12z/mov-imm-reloc.s: New file.
	* testsuite/gas/s12z/s12z.exp: Add them.