stmmac: dwmac-mediatek: fix clock issue

The pm_runtime takes care of the clock handling in current
stmmac drivers, and dwmac-mediatek implement the
mediatek_dwmac_clks_config() as the callback for pm_runtime.

Then, stripping duplicated clocks handling in old init()/exit()
to fix clock issue in suspend/resume test.

As to clocks in probe/remove, vendor need symmetric handling to
ensure clocks balance.

Test pass, including suspend/resume and ko insertion/remove.

Fixes: 3186bdad ("stmmac: dwmac-mediatek: add platform level clocks management")
Signed-off-by: Biao Huang <biao.huang@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>