arm: add basic mitigation for Cortex-A AES errata

arm: add basic mitigation for Cortex-A AES errata

This patch adds the basic patterns for mitigation of the erratum, but no
attempt is made at this point to optimize the results for the cases where
the erratum mitigation is not needed.

The mitigation is done by guaranteeing that the input operands are fed
from a full-width operation by using an identity operation on the input
values.

gcc/ChangeLog:

	* config/arm/crypto.md (crypto_<CRYPTO_AES:crypto_pattern>): Convert
	to define_expand.  Add mitigation for the Cortex-A AES erratum
	when enabled.
	(*crypto_<CRYPTO_AES:crypto_pattern>_insn): New pattern, based
	on original crypto_<CRYPTO_AES:crypto_pattern> insn.
	(aes_op_protect): New pattern.
	* config/arm/unspecs.md (unspec): Add UNSPEC_AES_PROTECT.