tegra: dc: Update dt-binding doc for new bindings

tegra: dc: Update dt-binding doc for new bindings

1. Add dt entry to make the default color space
as adobeRGB.
2. While parsing this entry make default as sRGB
if entry not found. This is to make it backward
compatible.
3. Update the devicetree binding doc for
nvidia,default_color_space, nvidia,cmu-lut1 and
cmu_adobe_rgb dt entries

Bug 1649854

Change-Id: Ic3fd44630ad64f80894ab2c52ac6021b8294a6a6
(cherry picked from commit 05296e421abfc5c1e4354d7b4ed93ad069c7e150)
Reviewed-on: http://git-master/r/747956
Signed-off-by: Arun Swain <arswain@nvidia.com>
Reviewed-on: http://git-master/r/783731
Reviewed-by: Mitch Luban <mluban@nvidia.com>
Tested-by: Mitch Luban <mluban@nvidia.com>