hwf-arm: add detection of ARMv8 crypto extension by toolchain config

* src/hwf-arm.c (detect_arm_hwf_by_toolchain): New.
(_gcry_hwf_detect_arm): Move __ARM_NEON check to
'detect_arm_hwf_by_toolchain' and add call to the new function.

This allows use of HW accelerated AES/SHA1/SHA256/GCM implementations
on macOS/aarch64 target.

• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>