[arm] avoid aes-1742098 mitigation in combine tests

[arm] avoid aes-1742098 mitigation in combine tests

The expected asm output for aes-fuse-[12].c does not correspond to
that which is generated when -mfix-cortex-a57-aes-1742098 is enabled.
The mitigation was introduced after the test, and enabled by default
for the selected processor, a72.  Select a53 instead, where the
migitation is not enabled by default, and all the expected fusions can
take place.

for  gcc/testsuite/ChangeLog

	* gcc.target/arm/aes-fuse-1.c: Switch to -mcpu=cortex-a53.
	* gcc.target/arm/aes-fuse-2.c: Likewise.