ir_aarch64.c contains tests that require extensions such as FP16

[egrimley-arm]

The tests in ir_aarch64.c that require extensions such as FP16 should presumably be moved to other files such as ir_aarch64_v82.c.

This isn't just for tidyness: code_api|api.ir currently fails on hardware without FP16. I thought it would be possible to make it pass by inserting a call to enable_all_test_cpu_features() but that turned out to be more difficult than I expected: I think the test is not linked with the right library for that.

I have a PR (#6433) that move the LDAPR tests out of ir_aarch64.c. After that I think the only feature required by that file is FP16. I think there is also a false dependency on FP16 due to #6432.