PCI: rockchip: Split out common function to init controller

Most of the initialization are used for both of RC driver and
EP driver; factor the initialization out to a new function,
rockchip_pcie_init_port(), in pcie-rockchip.c and rename the
original function to rockchip_pcie_host_init_port() to avoid
confusion. No functional changed intended.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Tested-by: Jeffy Chen <jeffy.chen@rock-chips.com>