These drivers only have runtime but no build time dependencies so can be
built for testing purposes if the Kconfig COMPILE_TEST option is enabled.

This is useful to have more build coverage and make sure that drivers are
not affected by changes that could cause build regressions.
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>