mtd: remove h720x flash support

The h720x platform support is going away in linux-3.10, so the
MTD driver will also not be needed any more.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>