Add the definition for S3C_GPIO_END to allow the PM code to build.

This means moving the GPIO bank numbers to a separate file to allow
the gpio and regs-gpio to include them. Including regs-gpio.h into
gpio.h causes too many build problems and adding gpio.h would mean
editing a large number of files.
Signed-off-by: Ben Dooks <ben-linux@fluff.org>