drm/msm/sde: Add 1D LUT IGC support for LUT_LAST

Adjust igc setup to include LUT_LAST for version 6.
The LUT_LAST entry is used to program the final lut entry. This
change also creates a common function for version 5 and 6 to
call to avoid repeating code.

Change-Id: I0ca9be1a65b6889afa7e16016b7094ad90930d57
Signed-off-by: Samantha Tran <samtran@codeaurora.org>