drm/bridge: Add helper to reset bridge pipeline

drm/bridge: Add helper to reset bridge pipeline

Let's provide an helper to make it easier for bridge drivers to
power-cycle their bridge.

In order to avoid a circular dependency between that new helper and
drm_atomic_helper_reset_crtc(), this new helper will be in a
drm_bridge_helper.c file to follow the pattern we have for other
objects.

Reviewed-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Tested-by: Herve Codina <herve.codina@bootlin.com>
Co-developed-by: Simona Vetter <simona.vetter@intel.com>
Signed-off-by: Simona Vetter <simona.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250313-bridge-connector-v6-8-511c54a604fb@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>