[IA64] Drop duplicated "config IOMMU_HELPER"

One entry for this in arch/ia64/Kconfig should be enough.
Reported-by: Christoph Egger <siccegge@cs.fau.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/Kconfig

@@ -59,9 +59,6 @@ config NEED_DMA_MAP_STATE
 config SWIOTLB
        bool
 
-config IOMMU_HELPER
-       bool
-
 config GENERIC_LOCKBREAK
 	def_bool n