msm: gsi: enable IEOB interrupts on MHI mode

Configure IEOB interrupts for MHI channels. Don't handle
these interrupts since handling is needed only for GPI
channels.

CRs-Fixed: 1097871
Change-Id: I6074486a1c858765b069197bf6b0c39d920c270b
Signed-off-by: Amir Levy <alevy@codeaurora.org>