staging: mt7621-dts: set up only two pcie phys

staging: mt7621-dts: set up only two pcie phys

This soc has only two real pcie phys one of them
having a different register to enable and disable it.
Change this to have only two dt nodes for the phys and
use 'phy-cells' properly to say if the phy has dual ports.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20200320110123.9907-3-sergio.paracuellos@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>