drm/panel/raspberrypi-touchscreen: Initialise the bridge in prepare

drm/panel/raspberrypi-touchscreen: Initialise the bridge in prepare

[ Upstream commit 5f18c0782b99e26121efa93d20b76c19e17aa1dd ]

The panel has a prepare call which is before video starts, and an
enable call which is after.
The Toshiba bridge should be configured before video, so move
the relevant power and initialisation calls to prepare.

Fixes: 2f733d6194bd ("drm/panel: Add support for the Raspberry Pi 7" Touchscreen.")
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220415162513.42190-3-stefan.wahren@i2se.com
Signed-off-by: Sasha Levin <sashal@kernel.org>