UdfpsHelper: Avoid hardcoding 4095 for maximum panel brightness

Now the array's last key is treated as maximum panel brightness
which should be the same as what's found in display devicetree
as maximum brightness for the specific panel.

Also remove the first few entries that are unused especially the
first erratic entry which sets the alpha to 255.

Change-Id: I5674d563e733a7485f75d744b0c110d551d66c1a