riscv: Update Microchip MPFS Icicle Kit support

This patch updates Microchip MPFS Icicle Kit support. For now,
add Microchip I2C driver, set environment variables for
mac addresses and default build for SBI_V02.

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