USB: gadget: Bringin QCOM specific changes to ACM driver

ACM function driver uses newly introduced function framework
which allows it to be independently built and also support
CONFG_FS based compositions.
Android composite driver uses get_(or put_)function framework
APIs to get the instance and function allocated and is responsible
for adding function to the composition using usb_add_function which
earlier was done by function drivers only.

Add QCOM specific changes to support multiple transports with ACM
e.g. SMD, SDIO, HSIC etc along with tty. Also add device sysfs
attributes to allow userspace to pass the transport binding
information.

Change-Id: I419d68e4f09003a75179c31155c932d5a73fd45e
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>