Serial : AT91 : Enable PDC and DMA RXBRK

The receiver detects a break condition when all data, parity and stop bits are low.
The PDC or DMA detect the RXBRK bit in US_CSR and enable RXBRK interrput, and meantime pdc or dma rx calculate the
break count.
A break condition will last for a specific duration, the receive data will be ignored during the duration.

Signed-off-by: Elen Song <elen.song@atmel.com>
Serial: AT91: Distinguish usart and uart

Distinguish usart and uart by read ip name register,
dbgu regards as uart.

Signed-off-by: Elen Song <elen.song@atmel.com>
Serial: AT91: Modify UART to use software timer to trigger rx

Signed-off-by: Elen Song <elen.song@atmel.com>
Serial: 5serial: Enable CTSIC interrupt when CTS is enabled

Only CTS pin configured that CTSIC should be triggered,
To avoid conficts, when enable CTS or RTS, these pins should not use as other functions simultaneous.

Signed-off-by: Elen Song <elen.song@atmel.com>
Serial: AT91: Only AT91RM9200 support DCDIC DSRIC RIIC

Signed-off-by: Elen Song <elen.song@atmel.com>