kernel: fix rtl8261n driver for non-realtek chips

kernel: fix rtl8261n driver for non-realtek chips

Part of the phy patch process breaks functionality on non-Realtek
platforms. Only apply this on Realtek SoCs to fix functionality
everywhere else.

Signed-off-by: Andrew LaMarche <andrewjlamarche@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21777
Signed-off-by: Robert Marko <robimarko@gmail.com>
(cherry picked from commit 268a0cb3633de760c1eddb4afdae4988bcabe3af)
Link: https://github.com/openwrt/openwrt/pull/21799
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>