msm: kgsl: Provide support for Limits Management upper value

Create dtsi entry for Limits Management value. Expose debugfs
inode 'lm_limit' for changing upper limit value in mA on the fly:
echo 2000 > lm_limit

Change-Id: Ia1be13e153bb1ac3eb1449817e1edf1b6c48c4cf
Signed-off-by: Oleg Perelet <operelet@codeaurora.org>