When allocating a frame buffer, the number of bits per pixel needed is
derived from the deprecated drm_format_info.cpp[] field.  While this may
work for formats using less than 8 bits per pixel, it does lead to a
large overallocation.

Reduce memory consumption by using the actual number of bits per pixel
instead.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/eabcf4f298184dabe46823fcf5ceffa1da0ec7ef.1657294931.git.geert@linux-m68k.org