drm/omapdrm: Fix console with deferred ops

Commit 95da53d6 ("drm/omapdrm: Use regular fbdev I/O helpers")
stopped console from updating for command mode displays because there is
no damage handling in fb_sys_write() unlike we had earlier in
drm_fb_helper_sys_write().

Let's fix the issue by adding FB_GEN_DEFAULT_DEFERRED_DMAMEM_OPS and
FB_DMAMEM_HELPERS_DEFERRED as suggested by Thomas. We cannot use the
FB_DEFAULT_DEFERRED_OPS as fb_deferred_io_mmap() won't work properly
for write-combine.

Fixes: 95da53d6 ("drm/omapdrm: Use regular fbdev I/O helpers")
Suggested-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240228063540.4444-3-tony@atomide.com