phy: xilinx: add runtime PM support

Added Runtime power management support to the xilinx phy driver and using
DEFINE_RUNTIME_DEV_PM_OPS new macros allows the compiler to remove the
unused dev_pm_ops structure and related functions if !CONFIG_PM without
the need to mark the functions __maybe_unused.

Signed-off-by: Piyush Mehta <piyush.mehta@amd.com>
Link: https://lore.kernel.org/r/20230613140250.3018947-2-piyush.mehta@amd.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>