drm/ast: Store CRTC memory request threshold in device quirks

drm/ast: Store CRTC memory request threshold in device quirks

Store each hardware's CRTC memory threshold in the specific instance
of struct ast_device_quirks. Removes the calls to IS_AST_GENn() from
ast_set_crtthd_reg().

The values stored in the registers appear to be plain limits. Hence
write them in the driver in decimal format instead of hexadecimal.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://lore.kernel.org/r/20251007150343.273718-4-tzimmermann@suse.de