PCI: rockchip: Split out rockchip_pcie_parse_dt() to parse DT

Most of the DT properties are used for both of RC driver and EP driver,
so split them out in a new function, rockchip_pcie_parse_dt(), in
pcie-rockchip.c and rename the original function to
rockchip_pcie_parse_host_dt() 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>