ARC: Add support for basic QEMU platform for ARC EM & HS

Now when we're finally ready to open QEMU port for ARC
we introduce the first ever platform it supports and in fact does
that quite well - Zephyr RTOS.

For now we only offer support of basic EM & HS code execution,
built-in timers, interrupt controller and set of very simple
peripherals: DW UART & optionally MMIO Virtio devices.

Signed-off-by: Wayne Ren <wei.ren@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>