drm/vc4: convert to devm_drm_bridge_alloc() API

drm/vc4: convert to devm_drm_bridge_alloc() API

This is the new API for allocating DRM bridges.

This driver already implements refcounting of the struct vc4_dsi, which
embeds struct drm_bridge. Now this is a duplicate of the refcounting
implemented by the DRM bridge core, so convert the vc4_dsi_get/put() calls
into drm_bridge_get/put() calls and get rid of the driver-specific
refcounting implementation.

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Acked-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250424-drm-bridge-convert-to-alloc-api-v2-27-8f91a404d86b@bootlin.com
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>