ARM i.MX53: tqma53: rev 300 specific pin configuration

I2S_MCLK is moved from pad GPIO19 to GPIO0, which can be muxed to the
ssi_ext1 clock signal. #SYSTEM_DOWN is moved from pad GPIO0 to GPIO19.
Add #PHY_RESET and LCD_CONTRAST.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>