[ARM] Support ARMv8.2 FP16 simd instructions

[ARM] Support ARMv8.2 FP16 simd instructions

gas/
	* config/tc-arm.c (N_S_32): New.
	(N_F_16_32): Likewise.
	(N_SUF_32): Support N_F16.
	(N_IF_32): Likewise.
	(neon_dyadic_misc): Likewise.
	(do_neon_cmp): Likewise.
	(do_neon_cmp_inv): Likewise.
	(do_neon_mul): Likewise.
	(do_neon_fcmp_absolute): Likewise.
	(do_neon_step): Likewise.
	(do_neon_abs_neg): Likewise.
	(CVT_FLAVOR_VAR): Likewise.
	(do_neon_cvt_1): Likewise.
	(do_neon_recip_est): Likewise.
	(do_vmaxnm): Likewise.
	(do_vrint_1): Likewise.
	(neon_check_type): Check architecture support for FP16 extension.
	(insns): Update comments.
	* testsuite/gas/arm/armv8-2-fp16-simd.s: New test source.
	* testsuite/gas/arm/armv8-2-fp16-simd.d: New testcase for arm mode.
	* testsuite/gas/arm/armv8-2-fp16-simd-thumb.d: Likewise for thumb mode.
	* testsuite/gas/arm/armv8-2-fp16-simd-warning.d: New rejection test for
	arm mode.
	* testsuite/gas/arm/armv8-2-fp16-simd-warning-thumb.d: Likewise for
	thumb mode.
	* testsuite/gas/arm/armv8-2-fp16-simd-warning.l: New expected rejection
	error file.

opcode/
	* arm-dis.c (neon_opcodes): Support new FP16 instructions.