[BUG] mt7986 doesn't allow to re-enable ethsys clock gates after they have been disabled

[Eugene Konev]

When ethsys clocks (eth_fe_en, eth_gp1_en, eth_gp2_en, eth_wocpu1_en and
eth_wocpu0_en) are disabled calling clk_enable on them doesn't enable them
again (appropriate bits in the register stay 0).
This prevents using mtk_eth as module, because kernel disables all unclaimed
clocks with clk_disable_unused.