PCI: armada8k: Add PHYs support

Bring PHY support for the Armada8k driver.

The Armada8k IP only supports x1, x2 or x4 link widths. Iterate over
the DT 'phys' entries and configure them one by one. Use
phy_set_mode_ext() to make use of the submode parameter (initially
introduced for Ethernet modes). For PCI configuration, let the submode
be the width (1, 2, 4, etc) so that the PHY driver knows how many
lanes are bundled. Do not error out in case of error for compatibility
reasons.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>