arm64: dts: rockchip: add gmac needed pclk for rk3399 pd

This patch fixes that sometimes hang at start-up time of the system.
As the below log:
...
[   11.136543] calling  pm_genpd_debug_init+0x0/0x60 @ 1
[   11.141602] initcall pm_genpd_debug_init+0x0/0x60 returned 0 after 11 usecs
[   11.148558] calling  genpd_poweroff_unused+0x0/0x84 @ 1
<hang>

In some cases, the rk3399 should turn off the gmac power domain to save
power if some boards didn't register the gmac device node for rk3399.
Then, rk3399 need to make sure the gmac's pclk enabled if we need
operate the gmac power domain. (Due to the NOC had enabled always)

Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>