Add usart driver for kernel serial.c
Delete serial.c and serial.h at /
Signed-off-by: wangzw <wangzw@yuettak.com>
"complete usart dma"
Merge serial driver, and fix some problem
Fix usart driver for usart2 and usart3
1. usart2 support int rx and dma tx
2. usart3 support int rx and dma tx
Fix some bug for serial device driver
Fix some bug
1. compile for keil
2. dma tx ringbuffer