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>
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 61eb468..b3bd5c6 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -23,6 +23,13 @@
 	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