disp: msm: sde: add msgq support for sde vm layer

Linux message queues(msgq) are used to communicate between VM's
This change creates a display specific msgq and a set of
framework api's for the VM layer to invoke communication
between the VMs'.

Display msgq is bidirectional. Tx end is created by default for
both the VM's. Rx is kept optional to avoid unnecessary creation
of listener threads.

Change-Id: If4e6410045293d6b21087a76ec018d4784dd5238
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>