sh_eth: Remove dummy Runtime PM callbacks

sh_eth: Remove dummy Runtime PM callbacks

Since commit 63d00be69348fda4 ("PM: runtime: Allow unassigned
->runtime_suspend|resume callbacks"), unassigned
.runtime_{suspend,resume}() callbacks are treated the same as dummy
callbacks that just return zero.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Tested-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://patch.msgid.link/ab2a8bb51eb7d02426f4072c27523c8f41ac1ad4.1756998732.git.geert+renesas@glider.be
Signed-off-by: Jakub Kicinski <kuba@kernel.org>