ARC: HSDK: add reset for EHCI

Add reset phandle to EHCI device tree node to make on-chip reset
controller usable with EHCI.

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