arc: Add support for HS Development Kit board

ARC HS Development Kit board is a new low-cost
development platform sporting ARC HS38 in real silicon
with nice set of features such as:
 * Quad-core ARC HS38 with 512 kB L2 cache and running @1GHz
 * 4Gb of DDR (we use only lowest 1Gb out of it now)
 * Lots of DesigWare peripherals
 * Different connectivity modules:
     - Synopsys HAPS HT3
     - Arduino-compatible connector
     - MikroBUS

This initial commit supports the following peripherals:
 * UART (DW 8250)
 * Ethernet (DW GMAC)
 * SD/MMC (DW Mobile Storage)
 * USB 1.1 & 2.0

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