drm/i915: Change intel_fbdev_fb_alloc() return type

drm/i915: Change intel_fbdev_fb_alloc() return type

Change intel_fbdev_fb_alloc() to return struct intel_fb instead
of struct drm_framebuffer. Let's us eliminate some annoying
aliasing variables in the fbdev setup code.

v2: Assing the results to the correct variable (Jani)
    Fix xe's copy

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240510102233.25057-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>