ARM: 7135/1: ep93xx: bring back missing <mach/gpio.h>

Change bd5f12a (ARM: 7042/3: mach-ep93xx: break out GPIO driver specifics)
accidentally removed the ep93xx <mach/gpio.h> instead of making it an empty
file. This causes compilation to fail:

In file included from include/linux/gpio.h:18:0,
                  from drivers/gpio/gpiolib.c:10:
linux/arch/arm/include/asm/gpio.h:5:23: fatal error: mach/gpio.h: No such file or directory
compilation terminated.
make[2]: *** [drivers/gpio/gpiolib.o] Error 1

Fix this by adding the file back.

Acked-by: Linus Walleij <[email protected]>
Acked-by: H Hartley Sweeten <[email protected]>
Cc: Ryan Mallon <[email protected]>
Signed-off-by: Mika Westerberg <[email protected]>
Signed-off-by: Russell King <[email protected]>

arch/arm/mach-ep93xx/include/mach/gpio.h

@@ -0,0 +1 @@
+/* empty */