drm/i915/display: remove unused intel-mid.h include

Nothing from intel-mid.h and this is only available on x86, so remove it
as we prepare support for other architectures.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211007233212.3896460-4-lucas.demarchi@intel.com