UART drivers.
- uart_dev_mtk.[ch] are the old-style Mediatek/Ralink-specific UART driver
as also found in sys/mips/rt305x/uart_dev_rt305x.c, with minor improvements
and FDT attachment enabled for the appropriate SoCs.
- uart_dev_mtk_ns8250.c is the new-style ns16550a-compatible UART driver
found in newer Mediatek SoCs. It uses the uart_dev_ns8250.c driver
indirectly and is basically just a wrapper around it and only overrides its
probe method.
The reason I am not using the uart_dev_ns8250.c driver directly is because
I have some code that does UART clock detection before initializing the
UART, so that we don't need to hard-code the UART clock frequency in the
dts files for each board.
Approved by: adrian (mentor)
Sponsored by: Smartcom - Bulgaria AD
Differential Revision: https://reviews.freebsd.org/D5840
