msm: mdss: Add high_perf flag to run H/W at highest capability

Adding a performance flag in perf_tune params to run the
H/W at its peak. Useful for debugging from the user side.
Give following command in adb shell to turn it on:
echo 1 > /sys/kernel/debug/mdp/perf/perf_mode
To turn off:
echo 0 > /sys/kernel/debug/mdp/perf/perf_mode

Change-Id: I11d86b840952b9f1d167e426997d50caa35b35cf
Signed-off-by: Vineet Bajaj <vbajaj@codeaurora.org>