dim: loosen some drm-intel checkpatch rules

Set max line length to 100. I don't want to silence the LONG_LINE
warning altogether, and I'd still prefer to keep lines under 80
characters, but I also don't want to see all the noise, and nor do I
want to see silly code trying to arbitrarily squeeze under 80 when it
doesn't make sense. 100 is a nice arbitrary round number... I hope
review catches silly stuff regardless. Fingers crossed.

BIT_MACRO. We have (1 << N) all over the place. I hope to switch to
BIT() macro eventually, but this documents current use.

PREFER_KERNEL_TYPES. We also have uint(8|16|32|64)_t all over the
place. I also hope to move towards kernel types, but this documents
current use.

SPLIT_STRING, LONG_LINE_STRING. Don't nag about strings split to many
lines, but also don't nag about strings not split.

There's plenty more that could be tweaked, but let's start with
something to improve the S/N ratio of the automated CI checkpatch
reports. Now that we have --show-types included in the output, we can
more easily discuss the ignores on a case-by-case basis.

Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>