aarch64: Improve mcpu/march conflict check

aarch64: Improve mcpu/march conflict check

Features from a cpu or base architecture that were explicitly disabled
by a +nofeat option were being incorrectly added back in before checking
for conflicts between -mcpu and -march options.  This patch instead
compares the returned feature masks directly.

gcc/ChangeLog:

	* config/aarch64/aarch64.cc (aarch64_override_options): Compare
	returned feature masks directly.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/target_attr_crypto_ice_1.c: Prune warning.
	* gcc.target/aarch64/target_attr_crypto_ice_2.c: Ditto.