drm/fourcc: Add DRM_FORMAT_D[1248]

drm/fourcc: Add DRM_FORMAT_D[1248]

As Rn covers single-channel formats with a direct relationship between
channel value and brightness, and Cn can be any colors, there are
currently no fourcc codes to describe single-channel formats with an
inverse relationship between channel value and brightness.

Introduce fourcc codes for a single-channel frame buffer format with
two, four, sixteen, or 256 brightness ("darkness") levels, where there
is an inverse relationship between channel value and brightness.

As the number of bits per pixel may be less than eight, some of these
formats rely on proper block handling for the calculation of bits per
pixel and pitch.

The fill order (the order in which multiple pixels are packed in a byte)
is the same order as used for grayscale (2, 4, and 16 levels) images in
the PNG specification, Version 1.2.
This order is also the recommended and default order (FillOrder = 1) for
bilevel and grayscale (16 levels) images in the TIFF 6.0 Specification,
and is also used for monochrome images in the PBM file format,
monochrome Linux frame buffer logos, and BDF and PSF (Linux kernel) font
files.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/6119f3abeda9baaa88652843960adc032da276b4.1657294931.git.geert@linux-m68k.org