ARM: SAMSUNG: Remove empty gpio-core.h and use central plat/gpio-core.h

Rename mach-s3c2410/include/mach/gpio-core.h to mach/gpio-track.h so that
it can be included by <plat/gpio-core.h> when needed.

Eliminate all other empty gpio-core.h files and just include the
<plat/gpio-core.h> as necessary.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>