MIPS: dts: loongson64g-package: Switch to Loongson UART driver

MIPS: dts: loongson64g-package: Switch to Loongson UART driver

Loongson64g is Loongson 3A4000, whose UART controller is compatible with
Loongson 2K1500, which is NS16550A-compatible with an additional
fractional frequency divisor register.

Update the compatible strings to reflect this, so that 3A4000 can
benefit from the fractional frequency divisor provided by loongson-uart.
This is required on some devices, otherwise their UART can't work at
some high baud rates, e.g., 115200.

Tested on Loongson-LS3A4000-7A1000-NUC-SE with a 25MHz UART clock.
Without fractional frequency divisor, the actual baud rate was 111607
(25MHz / 16 / 14, measured value: 111545) and some USB-to-UART
converters couldn't work with it at all. With fractional frequency
divisor, the measured baud rate becomes 115207, which is quite accurate.

Signed-off-by: Rong Zhang <rongrong@oss.cipunited.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>