msm: mhi_dev: Remove MHI hardware channel to IPA GSI mapping

Currently the MHI device driver maps the MHI hardware channel
with IPA's GSI channel. This can be done directly by IPA and
reduces the dependency between the two modules.

Change-Id: Ib51b2a264fdc69418889d2ebdbf1db823edf33be
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>