[bsp/wch/arm/Libraries/ch32_drivers/drv_pwm_ch32f10x.c]:support pwm.

[bsp/wch/arm/ch32f103c8-core]:add timer1~4(include 4 channel) pwm.

Author: charlown

bsp/wch/arm/Libraries/ch32_drivers/SConscript

@@ -32,6 +32,9 @@ if  GetDepend('SOC_ARM_SERIES_CH32F103'):
     if GetDepend(['RT_USING_HWTIMER', 'BSP_USING_HWTIMER']):
         src += ['drv_hwtimer_ch32f10x.c']
 
+    if GetDepend(['RT_USING_PWM', 'BSP_USING_PWM']):
+        src += ['drv_pwm_ch32f10x.c']
+
 src += ['drv_common.c']
 
 path =  [cwd]