drm/panel-simple: Add a timing for the Raspberry Pi 7" panel

The Raspberry Pi 7" 800x480 panel uses a Toshiba TC358762 DSI
to DPI bridge chip, so there is a requirement for the timings
to be specified for the end panel. Add such a definition.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>