pwm: Add PWM driver for SiFive SoC

Adds a PWM driver for PWM chip present in SiFive's HiFive Unleashed SoC
This driver is simple port of Linux pwm sifive driver from Linux v5.6

commit: 9e37a53eb051 ("pwm: sifive: Add a driver for SiFive SoC PWM")

Signed-off-by: Yash Shah <yash.shah@sifive.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index edb3f0f..61eb468 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -47,6 +47,12 @@
 	  useful. The PWM can be enabled but is not connected to any outputs
 	  so this is not very useful.
 
+config PWM_SIFIVE
+	bool "Enable support for SiFive PWM"
+	depends on DM_PWM
+	help
+	  This PWM is found SiFive's FU540 and other SoCs.
+
 config PWM_TEGRA
 	bool "Enable support for the Tegra PWM"
 	depends on DM_PWM