phy: adin: add support for clock output

The ADIN1300 supports generating certain clocks on its GP_CLK pin, as
well as providing the reference clock on CLK25_REF.

Add support for selecting the clock via device-tree properties.

This patch is based on the Linux implementation for this feature,
which has been added to netdev/net-next.git [1].

[2] https://patchwork.kernel.org/project/netdevbpf/cover/20220517085143.3749-1-josua@solid-run.com/



Signed-off-by: Josua Mayer <josua@solid-run.com>