net: mvpp2: add EEE implementation

Add EEE support for mvpp2, using phylink's EEE implementation, which
means we just need to implement the two methods for LPI control, and
with the initial configuration. Only SGMII mode is supported, so only
100M and 1G speeds.

Disabling LPI requires clearing a single bit. Enabling LPI needs a full
configuration of several values, as the timer values are dependent on
the MAC operating speed.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/E1tYAE0-0014Pz-R9@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>