mhi: core: add support for using pre-mapped buffers for data transfer

Some MHI clients already pre-map the buffer before passing it to MHI
core layer. They do this when using memory reclaim algorithms and
wants to avoid mapping and unmapping buffers after each transfer.

CRs-Fixed: 2361266
Change-Id: If78d66c77c6887a1841a4d94108052e26b07c231
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>