pwm: Add driver for Amlogic Meson PWM controller

This adds the driver for the PWM controller found in the Amlogic SoCs.

This PWM is only a set of Gates, Dividers and Counters:
PWM output is achieved by calculating a clock that permits calculating
two periods (low and high). The counter then has to be set to switch after
N cycles for the first half period.
The hardware has no "polarity" setting. This driver reverses the period
cycles (the low length is inverted with the high length) for
PWM_POLARITY_INVERSED.

Disabling the PWM stops the output immediately (without waiting for the
current period to complete first).

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>

drivers/pwm/Kconfig

@@ -23,6 +23,13 @@ config PWM_IMX
 	help
 	  This PWM is found i.MX27 and later i.MX SoCs.
 
+config PWM_MESON
+	bool "Enable support for Amlogic Meson SoCs PWM"
+	depends on DM_PWM
+	help
+	  This PWM is found on Amlogic Meson SoCs. It supports a
+	  programmable period and duty cycle for 2 independant channels.
+
 config PWM_MTK
 	bool "Enable support for MediaTek PWM"
 	depends on DM_PWM

drivers/pwm/Makefile

@@ -12,6 +12,7 @@ obj-$(CONFIG_DM_PWM)		+= pwm-uclass.o
 
 obj-$(CONFIG_PWM_EXYNOS)	+= exynos_pwm.o
 obj-$(CONFIG_PWM_IMX)		+= pwm-imx.o pwm-imx-util.o
+obj-$(CONFIG_PWM_MESON)		+= pwm-meson.o
 obj-$(CONFIG_PWM_MTK)		+= pwm-mtk.o
 obj-$(CONFIG_PWM_ROCKCHIP)	+= rk_pwm.o
 obj-$(CONFIG_PWM_SANDBOX)	+= sandbox_pwm.o