ARM: dts: imx25-pinfunc: add config for kpp rows 4 to 7

i.MX25's Keypad Port (KPP) can be used with a key pad matrix of up to
8 x 8 keys. Add pin configurations for rows 4 to 7.

The new defines have been tested on an out-of-tree board.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>