drm/i915/display: Remove preferred_bpp from struct intel_fbdev

drm/i915/display: Remove preferred_bpp from struct intel_fbdev

The value preferred_bpp in struct intel_fbdev duplicates preferred_bpp
in struct drm_fb_helper. Remove the former.

Instead let intel_fbdev_init_bios() read the framebuffer from the
hardware. Then derive preferred_bpp from its format and initialize
struct drm_fb_helper with the value. The default is 32 (i.e., XRGB8888).

Also removes one of those deprecated references to the cpp field of
struct drm_format_info.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241212170913.185939-8-tzimmermann@suse.de
Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>