net: phy: at803x: add LED support for qca808x

Add LED support for QCA8081 PHY.

Documentation for this LEDs PHY is very scarce even with NDA access
to Documentation for OEMs. Only the blink pattern are documented and are
very confusing most of the time. No documentation is present about
forcing the LED on/off or to always blink.

Those settings were reversed by poking the regs and trying to find the
correct bits to trigger these modes. Some bits mode are not clear and
maybe the documentation option are not 100% correct. For the sake of LED
support the reversed option are enough to add support for current LED
APIs.

Supported HW control modes are:
- tx
- rx
- link_10
- link_100
- link_1000
- link_2500
- half_duplex
- full_duplex

Also add support for LED polarity set to set LED polarity to active
high or low. QSDK sets this value to high by default but PHY reset value
doesn't have this enabled by default.

QSDK also sets 2 additional bits but their usage is not clear, info about
this is added in the header. It was verified that for correct function
of the LED if active high is needed, only BIT 6 is needed.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20240125203702.4552-6-ansuelsmth@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>