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/core.c b/drivers/pwm/core.c
index 3a7769f..f7c11d2 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -455,7 +455,7 @@
 	if (!pwm->chip->ops->set_polarity)
 		return -ENOSYS;
 
-	if (test_bit(PWMF_ENABLED, &pwm->flags))
+	if (pwm_is_enabled(pwm))
 		return -EBUSY;
 
 	err = pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
@@ -853,7 +853,7 @@
 		if (test_bit(PWMF_REQUESTED, &pwm->flags))
 			seq_puts(s, " requested");
 
-		if (test_bit(PWMF_ENABLED, &pwm->flags))
+		if (pwm_is_enabled(pwm))
 			seq_puts(s, " enabled");
 
 		seq_puts(s, "\n");