PCI: rockchip: Add Kconfig COMPILE_TEST

Allow selection of the Rockchip driver for compile testing, even if we
aren't building for ARCH_ROCKCHIP.

[bhelgaas: changelog]
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>