net: phy: add support for qca8k switch internal PHY in at803x

Since the at803x share the same regs, it's assumed they are based on the
same implementation. Make it part of the at803x PHY driver to skip
having redudant code.
Add initial support for qca8k internal PHYs. The internal PHYs requires
special mmd and debug values to be set based on the switch revision
passwd using the dev_flags. Supports output of idle, receive and eee_wake
errors stats.
Some debug values sets can't be translated as the documentation lacks any
reference about them.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>