Add precise vblank timestamp support through the DRM framework.
Implement the vblank related hooks to get the vblank count and
timestamp. Use MDSS 8.x, hardware feature that supports logging
of the vsync timestamp counter which can be used to derive the
accurate kernel timestamp. The current ktime would be returned
for older targets to support backward compatibility.
Change-Id: I2d35ed4a643a519e602278b6d16e67ccee16a60b
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>