USB: f_mbim: Add support for BAM-DMUX transport

BAM-DMUX transport is used for data path on targets which do not
have IPA hardware block. The u_bam module is used for interfacing with
BAM-DMUX. Add wrapper functions in u_bam to allocate the grmnet
dynamically while connecting to the port. This eliminates the need of
maintaining grmnet in mbim driver.

Change-Id: Ifc8db531d7e0090e63f31f2bf9994000e03109ea
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>