drm/bridge: tc358768: Add LP mode command support

drm/bridge: tc358768: Add LP mode command support

Currently the driver ignores MIPI_DSI_MODE_LPM and always uses HS mode.
Add code to enable HS mode in pre_enable() only if MIPI_DSI_MODE_LPM is
not set, and always enable HS mode in enable() for video transmission.

Tested-by: João Paulo Gonçalves <joao.goncalves@toradex.com> # Toradex Verdin AM62
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Link: https://patch.msgid.link/20260311-tc358768-v2-5-e75a99131bd5@ideasonboard.com
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>