ARM: ep93xx: move private headers out of mach/*

gpio-ep93xx.h, hardware.h, and platform.h are only used in
arch/arm/mach-ep93xx, so we can move them one there and no
longer expose them to device drivers.

Acked-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Olof Johansson <olof@lixom.net>