soc: rockchip: ROCKCHIP_GRF should not default to y, unconditionally

Merely enabling CONFIG_COMPILE_TEST should not enable additional code.
To fix this, restrict the automatic enabling of ROCKCHIP_GRF to
ARCH_ROCKCHIP, and ask the user in case of compile-testing.

Fixes: 4c58063d ("soc: rockchip: add driver handling grf setup")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210208143855.418374-1-geert+renesas@glider.be


Signed-off-by: Heiko Stuebner <heiko@sntech.de>