drm/mgag200: Store maximum resolution and memory bandwidth in device info

The maximum resolution and memory bandwidth are model-specific limits.
Both are used during display-mode validation. Store the values in struct
mgag200_device_info and simplify the validation code.

v2:
	* 'bandwith' -> 'bandwidth' in commit message

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220601112522.5774-9-tzimmermann@suse.de