msm: mdss: Disable bw release for cmd mode panels

For command mode panels, driver can release the bandwidth once
the frame is transferred to the panel and no more processing is
done in the display driver; in some scenarios this results in
more power consumption since more interrupts are generated.
This change disables the bandwidth release for command mode panels
and add a debugfs node to dynamically enable the feature if needed
for debugging purposes.
To enable the bw release:
echo 1 > "<debugfs>/mdp/perf/enable_bw_release"
To disable the bw release (default):
echo 0 > "<debugfs>/mdp/perf/enable_bw_release"

Change-Id: I61670606f1cf52b8d889678e6ffe7d0e911771e7
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>