fbcon: Remove fb_debug_enter/_leave from struct fb_ops

fbcon: Remove fb_debug_enter/_leave from struct fb_ops

There are no implementations of fb_debug_enter and fb_debug_leave.
Remove the callbacks from struct fb_ops and clean up the caller.

The field save_graphics in fbcon_par is also no longer required.
Remove it as well.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Acked-by: Daniel Thompson (RISCstar) <danielt@kernel.org>
Link: https://patch.msgid.link/20251125130634.1080966-6-tzimmermann@suse.de