ARC: reset: introduce AXS10x reset driver

ARC AXS10x boards support custom IP-block which allows to control
reset signals of selected peripherals. For example DW GMAC, etc...
This block is controlled via memory-mapped register (AKA CREG) which
represents up-to 32 reset lines. This regiter is self-clearing so we
don't need to deassert line after reset.

As of today only the following lines are used:
 - DW GMAC - line 5

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>