pwm: sunxi: add support for PWM found on Allwinner A64

This commit adds basic support for PWM found on Allwinner A64.
It can be used for pwm_backlight driver (e.g. for Pinebook)

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 16739e7..a837c35 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -15,3 +15,4 @@
 obj-$(CONFIG_PWM_ROCKCHIP)	+= rk_pwm.o
 obj-$(CONFIG_PWM_SANDBOX)	+= sandbox_pwm.o
 obj-$(CONFIG_PWM_TEGRA)		+= tegra_pwm.o
+obj-$(CONFIG_PWM_SUNXI)		+= sunxi_pwm.o