riscv: dts: Split Microchip device tree

The device tree split into .dtsi and .dts files, common
device node for eMMC/SD, enable I2C1, UART1 for console
instead of UART0, enable the DDR 2GB memory and in
that 288MB memory is reserved for fabric buffer.

Signed-off-by: Padmarao Begari <padmarao.begari@microchip.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>