pwm: Add the pwm_is_enabled() helper

Some PWM drivers are testing the PWMF_ENABLED flag. Create a helper
function to hide the logic behind enabled test. This will allow us to
smoothly move from the current approach to an atomic PWM update
approach.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
diff --git a/drivers/pwm/pwm-ep93xx.c b/drivers/pwm/pwm-ep93xx.c
index e593e9c..bbf10ae 100644
--- a/drivers/pwm/pwm-ep93xx.c
+++ b/drivers/pwm/pwm-ep93xx.c
@@ -82,7 +82,7 @@
 	 * The clock needs to be enabled to access the PWM registers.
 	 * Configuration can be changed at any time.
 	 */
-	if (!test_bit(PWMF_ENABLED, &pwm->flags)) {
+	if (!pwm_is_enabled(pwm)) {
 		ret = clk_enable(ep93xx_pwm->clk);
 		if (ret)
 			return ret;
@@ -113,7 +113,7 @@
 		ret = -EINVAL;
 	}
 
-	if (!test_bit(PWMF_ENABLED, &pwm->flags))
+	if (!pwm_is_enabled(pwm))
 		clk_disable(ep93xx_pwm->clk);
 
 	return ret;