aarch64: Add support for FEAT_SME_F16F16 fmla and fmls instructions.

This patch adds support for FEAT_SME_F16F16 instructions fmla and fmls,
which are available on passing command line flags +sme-f16f16 and the
spec is available here[1].
[1]: https://developer.arm.com/documentation/ddi0602/2024-06/SME-Instructions?lang=en