arm64: Move FP/ASIMD hwcap handling to common code

The FP/ASIMD is detected in fpsimd_init(), which is built-in
unconditionally. Lets move the hwcap handling to the central place.

Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
Tested-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>