phy: Add new PHY attribute max_link_rate

phy: Add new PHY attribute max_link_rate

Add new PHY attribute max_link_rate to struct phy_attrs. This indicates
maximum link rate supported by PHY (in Mbps).

Signed-off-by: Yuti Amonkar <yamonkar@cadence.com>
Signed-off-by: Swapnil Jakhade <sjakhade@cadence.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Link: https://lore.kernel.org/r/1599805114-22063-2-git-send-email-sjakhade@cadence.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>