msm: mdss: Add read/write buffer support for calibraiton tool

This change allows to process read/write operation through
buffer instead of single IOCTL call. It is part of
optimization to save DIAG packet processing time.

Change-Id: Iffaab2dd160959f8c7950ebca043b1e0cf25877c
Signed-off-by: Arpita Banerjee <cabane@codeaurora.org>