Input: mtk-pmic-keys - allow compiling with COMPILE_TEST

There are no hard architecture dependencies in the driver, so to improve
compile test coverage let's enable the driver when COMPILE_TEST is
selected.

Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/YowG7BVsJTNd0ELi@google.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>