ch569w-evt: add usbhs device mode driver
* usbd driver tested with cdc_vcom, internal loopback
(can't run both MSH & usbd due to 16KB RAM limitation)
* reduce usrstack & main thread stack size for usbd test
* ch56x_uart.c : iron out UART0_PIN_ALT assignment
WCH CH569W-R0-1v0 evt board bsp port, first version
dev/test under Ubuntu 20.04
toolchain from MounRiver_Studio_Community_Linux_x64_V120
tested drivers : SysTick, gpio, gpio interrupt, uart1 (RX interrupt, TX polling)
libcpu/risc-v/SConscript :
group includes rtconfig.CPU only if folder exists
libcpu/risc-v/common/cpuport.c/rt_hw_context_switch_interrupt() :
make it RT_WEAK for customization
emuzit