realtek: pcs: rtl931x: merge and drop unused helper
Merge the unused helper 'rtpcs_931x_sds_fiber_disable' into Fiber mode
setting, and drop the helper itself. As with the MII helper in a
previous commit, functionality is basically the same just with a value
for OFF mode. If functionality is required later, Fiber mode setting can
be used with the OFF mode instead of carrying the unused helper until
it's used.
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/20736
Signed-off-by: Robert Marko <robimarko@gmail.com>