mhi: core: Reduce interrupt moderation to 1ms

Reduce interrupt moderation for both inbound and outbound
hardware channels to 1ms, for improved latency response to
device acknowledgements.

CRs-Fixed: 782801
Change-Id: Id0717582d88dcfc12a8711f983da59a8f651b6d3
Signed-off-by: Andrei Danaila <adanaila@codeaurora.org>