arc: add AXS101 board support

AXS101 is a new generation of devlopment boards from Synopsys that houses
ASIC with ARC700 and lots of DesignWare peripherals:

 * DW APB UART
 * DW Mobile Storage (MMC/SD)
 * DW I2C
 * DW GMAC

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Francois Bedard <fbedard@synopsys.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Heiko Schocher <hs@denx.de>