[AArch64] Fix +nofp16 handling

[AArch64] Fix +nofp16 handling

Feature flag handling was not perfect, +nofp16 disabled fp
instructions too.

New feature flag macros were added to check features with multiple
bits set (matters for FP_F16 and SIMD_F16 opcode feature tests).
The unused AARCH64_OPCODE_HAS_FEATURE was removed, all checks should
use one of the AARCH64_CPU_HAS_* macros.  AARCH64_CPU_HAS_FEATURE
now checks all feature bits.

The aarch64_features table now contains the dependencies as
a separate field (so when the feature is enabled all dependencies
are enabled and when it is disabled everything that depends on it
is disabled).

Note that armv8-a+foo+nofoo is not equivalent to armv8-a if
+foo turns on dependent features that nofoo does not turn off.

gas/
	* config/tc-aarch64.c (struct aarch64_option_cpu_value_table): Add
	require field.
	(aarch64_features): Initialize require fields.
	(aarch64_parse_features): Handle dependencies.
	(aarch64_feature_enable_set, aarch64_feature_disable_set): New.
	(md_assemble): Use AARCH64_CPU_HAS_ALL_FEATURES.
	* testsuite/gas/aarch64/illegal-nofp16.s: New.
	* testsuite/gas/aarch64/illegal-nofp16.l: New.
	* testsuite/gas/aarch64/illegal-nofp16.d: New.

include/
	* opcode/aarch64.h (AARCH64_CPU_HAS_ALL_FEATURES): New.
	(AARCH64_CPU_HAS_ANY_FEATURES): New.
	(AARCH64_CPU_HAS_FEATURE): Define as AARCH64_CPU_HAS_ALL_FEATURES.
	(AARCH64_OPCODE_HAS_FEATURE): Remove.