MIPS: Only build microMIPS specific simulator functions if microMIPS support is required.
    
    This fixes PR sim/19441.  In the MIPS simulator the microMIPS
    functions in micromips.igen were not predicated on the microMIPS
    models.  This was causing build issues for some target triples.
    This patch sets all the microMIPS specific functions to only be built if
    the micromips32, micromips64 or micromipsdsp models are used.
    
    	PR sim/19441
    	* micromips.igen (delayslot_micromips): Enable for `micromips32',
    	`micromips64' and `micromipsdsp' only.
    	(process_isa_mode): Enable for `micromips32' and `micromips64' only.
    	(do_micromips_jalr, do_micromips_jal): Likewise.
    	(compute_movep_src_reg): Likewise.
    	(compute_andi16_imm): Likewise.
    	(convert_fmt_micromips): Likewise.
    	(convert_fmt_micromips_cvt_d): Likewise.
    	(convert_fmt_micromips_cvt_s): Likewise.
    	(FMT_MICROMIPS): Likewise.
    	(FMT_MICROMIPS_CVT_D): Likewise.
    	(FMT_MICROMIPS_CVT_S): Likewise.