mhi: core: set bei bit based on event ring intmod value

BEI bit should be set based on event ring intmod value in the
channel struct to allow easy pre-configured access when sending
out any packets. This allows device to respond directly to
packets without the need of waiting for interrupt moderation
time period.

Change-Id: Ib3814bef972bac254715b2d252d7f4bce776803a
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>