This driver works as a module, so mark it as a tristate config
instead of a bool.

Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: NStephen Boyd <sboyd@codeaurora.org>
Reviewed-by: NAndy Gross <agross@codeaurora.org>
Signed-off-by: NAndy Gross <agross@codeaurora.org>