net: ti: icssg-prueth: Add Power management support

Add suspend / resume APIs to support power management in ICSSG ethernet
driver.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Link: https://lore.kernel.org/r/20230801091428.1359979-11-danishanwar@ti.com
Signed-off-by: Nishanth Menon <nm@ti.com>