staging: mt7621-pci: fix reset lines for each pcie port

Depending of chip revision reset lines are inverted. It is also
necessary to read PCIE_FTS_NUM register before enabling the phy.
Hence update the code to achieve this.

Fixes: 745eeeac ("staging: mt7621-pci: factor out 'mt7621_pcie_enable_port' function")
Reported-by: NeilBrown <neil@brown.name>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Tested-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>