sh: ecovec24: modify tsc2007 platform settings

This patch modify x_plate_ohms to correct value for tsc2007 panel,
and removed un-necessary ts_get_pendown_state()

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>