uio: msm_sharedmem: Add new device driver for sharedmemory access

Add new device driver to provide a standard interface for its
clients (like RemoteFS and RFSA) to be able to memory map their
respective allotted shared memory address in the client's address space.
The shared memory (a transport buffer) address is unique for each
individual client and is made available to the driver via device tree.

This driver uses the existing UIO framework to facilitate the clients
mmap requirements. Each individual client will be able to use a unique
UIO device for this purpose.

Signed-off-by: Pratibhasagar V <pratibha@codeaurora.org>
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>