drivers: marvell: comphy-a3700: support SGMII COMPHY power off
drivers: marvell: comphy-a3700: support SGMII COMPHY power off

Add support for powering off the SGMII COMPHY (on lanes 0 and 1).
This is needed sometimes on Turris Mox when using KEXEC.

There is also another benefit of a little energy saving when the given
network interface is down.

Signed-off-by: Marek Behún <d64f4a2263a76be7ba227d043cc5b34c91f070db@nic.cz>
Change-Id: I55ae0fe3627e7cc0f65c78a00771939d8bf5399f

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware