net: 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.

Technically the phy also supports a recovered 125MHz clock for
synchronous ethernet. SyncE should be configured dynamically at
runtime, however Linux does not currently have a toggle for this,
so support is explicitly omitted.

Co-developed-by: Alvaro Karsz <alvaro.karsz@solid-run.com>
Signed-off-by: Alvaro Karsz <alvaro.karsz@solid-run.com>
Signed-off-by: Josua <Mayer&lt;josua@solid-run.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>