TI: DaVinci: GPIO header file and definitions

Some DaVinci SOC's use GPIOs to enable EMAC and DM9000.
This patch adds some definitions for GPIO registers and also adds
structures for GPIO.
A separate header file is being added so that in future we
can have a DaVinci GPIO driver similer to OMAP.

Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
Acked-by: Tom Rix <Tom.Rix@windriver.com>