vservices: block: add the block protocol and drivers

Adds the virtual services block protocol and block io drivers.
This protocol and drivers support exporting virtual block devices
from one VM to another, which are backed by another block device.

Change-Id: I47f86307c6201cb66d81bd453bb8c6c7ce99480f
Signed-off-by: Carl van Schaik <carl@cog.systems>
Git-commit: 9e55989babab087627e1ae42b2ed8e656c4b3993
Git-repo: https://github.com/CogSystems/linux-msm/commits/msm-4.9-hyp


Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>
[pheragu@codeaurora: Changing bio APIs]
Signed-off-by: Prakruthi Deepak Heragu <pheragu@codeaurora.org>
Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>