pwm: ti: am33xx: add enhanced pwm driver

Enhanced high resolution PWM module (EHRPWM) hardware can be used to
generate PWM output over 2 channels. This commit adds PWM driver support
for EHRPWM device present on AM33XX SOC.

The code is based on the drivers/pwm/pwm-tiehrpwm.c driver of the Linux
kernel version 5.9-rc7.
For DT binding details see:
- Documentation/devicetree/bindings/pwm/pwm-tiehrpwm.txt

Signed-off-by: Dario Binacchi <dariobin@libero.it>
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index f21ae7d..0b9d269 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -19,3 +19,4 @@
 obj-$(CONFIG_PWM_SIFIVE)	+= pwm-sifive.o
 obj-$(CONFIG_PWM_TEGRA)		+= tegra_pwm.o
 obj-$(CONFIG_PWM_SUNXI)		+= sunxi_pwm.o
+obj-$(CONFIG_PWM_TI_EHRPWM)	+= pwm-ti-ehrpwm.o