drm/atomic-helper: Separate out bridge pre_enable/post_disable from enable/disable

drm/atomic-helper: Separate out bridge pre_enable/post_disable from enable/disable

The encoder-bridge ops occur by looping over the new connector states of
the display pipelines. The enable sequence runs as follows -

	- pre_enable(bridge),
	- enable(encoder),
	- enable(bridge),

while the disable sequnce runs as follows -

	- disable(bridge),
	- disable(encoder),
	- post_disable(bridge).

Separate out the pre_enable(bridge), and the post_disable(bridge)
operations into separate functions each.

This patch keeps the sequence same for any singular disaplay pipe, but
changes the sequence across multiple display pipelines.

This patch is meant to be an interim patch, to cleanly pave the way for
the sequence re-ordering patch, and maintain bisectability in the
process.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Jayesh Choudhary <j-choudhary@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Tested-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
Tested-by: Devarsh Thakkar <devarsht@ti.com>
Link: https://lore.kernel.org/r/20250605171524.27222-3-aradhya.bhatia@linux.dev
Signed-off-by: Maxime Ripard <mripard@kernel.org>