arm: Remove iwmmxt support from arm.cc

arm: Remove iwmmxt support from arm.cc

TARGET_IWMMXT, TARGET_IWMMXT2 and their _REALLY_ equivalents are never
true now, so the code using them can be simplified.

gcc/ChangeLog:

	* config/arm/arm.cc (arm_option_check_internal): Remove
	IWMMXT check.
	(arm_options_perform_arch_sanity_checks): Likewise.
	(use_return_insn): Likewise.
	(arm_init_cumulative_args): Likewise.
	(arm_legitimate_index_p): Likewise.
	(thumb2_legitimate_index_p): Likewise.
	(arm_compute_save_core_reg_mask): Likewise.
	(output_return_instruction): Likewise.
	(arm_compute_frame_layout): Likewise.
	(arm_save_coproc_regs): Likewise.
	(arm_hard_regno_mode_ok): Likewise.
	(arm_expand_epilogue_apcs_frame): Likewise.
	(arm_expand_epilogue): Likewise.
	(arm_vector_mode_supported_p): Likewise.
	(arm_preferred_simd_mode): Likewise.
	(arm_conditional_register_usage): Likewise.