treewide: use linux/time.h for time conversion defines

Now that we have time conversion defines from in time.h there is no need
for each driver to define their own version.

Signed-off-by: Igor Prusov <ivprusov@salutedevices.com>
Reviewed-by: Svyatoslav Ryhel <clamor95@gmail.com> # tegra
Reviewed-by: Eugen Hristev <eugen.hristev@collabora.com> #at91
Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org> #qcom geni
Reviewed-by: Stefan Bosch <stefan_b@posteo.net> #nanopi2
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/drivers/pwm/pwm-mtk.c b/drivers/pwm/pwm-mtk.c
index 11e7444..ad845ed 100644
--- a/drivers/pwm/pwm-mtk.c
+++ b/drivers/pwm/pwm-mtk.c
@@ -12,6 +12,7 @@
 #include <div64.h>
 #include <linux/bitops.h>
 #include <linux/io.h>
+#include <linux/time.h>
 
 /* PWM registers and bits definitions */
 #define PWMCON			0x00
@@ -27,8 +28,6 @@
 #define PWM_CLK_DIV_MAX		7
 #define MAX_PWM_NUM		8
 
-#define NSEC_PER_SEC 1000000000L
-
 enum mtk_pwm_reg_ver {
 	PWM_REG_V1,
 	PWM_REG_V2,