mhi: core: Enable BB scheme for MHI

Enable bounce buffering scheme in MHI for the cases
where allocated APQ memory falls outside of the memory range
which the device can access.

Change-Id: I9f40b0dda2f49111b7deb22973e6399fada90094
Signed-off-by: Andrei Danaila <adanaila@codeaurora.org>