ARM: i.MX27: Add GPT devicetree nodes

The GPT is the GPT timer found on i.MX SoCs.

This adds the missing GPT devicetree nodes. Also fixup the watchdog
register map size along the way. it's 0x1000, not 0x4000. This didn't
hurt before as the region was not occupied by another device, but now
overlaps with the GPT.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>