octeon: enable AT803x PHY driver

octeon: enable AT803x PHY driver

The AR8035 PHY is used in most Octeon boards supported by OpenWRT (all
the Ubiquiti routers at least). To be able to use its PHY-specific
functionality (cable testing, LED Control, ...) it should be built on
Octeon. It also needs the regulator framework, so enable that as well.
These boards are not space-constrained, so this really has no downsides.

Tested on an EdgeRouter Lite, cable tests now work with ethtool-full.

Signed-off-by: Lorenz Brun <lorenz@brun.one>
Link: https://github.com/openwrt/openwrt/pull/17318
Signed-off-by: Robert Marko <robimarko@gmail.com>