clk: rockchip: allow COMPILE_TEST builds

clk: rockchip: allow COMPILE_TEST builds

COMMON_CLK_ROCKCHIP already gates the Rockchip clock objects inside the
Rockchip clock Makefile.  Allow selecting it for COMPILE_TEST and use it
for the parent Makefile descent instead of ARCH_ROCKCHIP.

The per-SoC Rockchip clock symbols already have COMPILE_TEST dependencies,
so this exposes the existing build coverage to other architectures without
selecting the Rockchip platform.

Tested with:
make LLVM=1 ARCH=loongarch drivers/clk/rockchip/

Assisted-by: Codex:GPT-5.5
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Brian Masney <bmasney@redhat.com>
Link: https://patch.msgid.link/20260509003602.956186-1-rosenp@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>