q800: drop 8-bit graphic_depth check for Apple 21 inch display

q800: drop 8-bit graphic_depth check for Apple 21 inch display

The graphic_depth check is no longer required since commit df8abbbadf ("macfb:
add common monitor modes supported by the MacOS toolbox ROM") which introduced
code in macfb_common_realize() to only allow the resolutions/depths provided in
macfb_mode_table to be specified for each display type.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Fixes: df8abbbadf ("macfb: add common monitor modes supported by the MacOS toolbox ROM")
Message-Id: <20211020141810.7875-1-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>