net: stmmac: dwmac-rk: fix unbalanced pm_runtime_enable warnings

This reverts commit 2c896fb0
"net: stmmac: dwmac-rk: add pd_gmac support for rk3399" and fixes
unbalanced pm_runtime_enable warnings.

In the commit to be reverted, support for power management was
introduced to the Rockchip glue code. Later, power management support
was introduced to the stmmac core code, resulting in multiple
invocations of pm_runtime_{enable,disable,get_sync,put_sync}.

The multiple invocations happen in rk_gmac_powerup and
stmmac_{dvr_probe, resume} as well as in rk_gmac_powerdown and
stmmac_{dvr_remove, suspend}, respectively, which are always called
in conjunction.

Fixes: 5ec55823

 ("net: stmmac: add clocks management for gmac driver")
Signed-off-by: Michael Riesch <michael.riesch@wolfvision.net>
Signed-off-by: David S. Miller <davem@davemloft.net>