iommu-helper: move the IOMMU_HELPER config symbol to lib/

This way we have one central definition of it, and user can select it as
needed.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 5cf611f..bd1cd84 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -222,6 +222,7 @@
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_VIRT_CPU_ACCOUNTING
 	select HAVE_IRQ_TIME_ACCOUNTING
+	select IOMMU_HELPER			if PPC64
 	select IRQ_DOMAIN
 	select IRQ_FORCED_THREADING
 	select MODULES_USE_ELF_RELA
@@ -477,9 +478,6 @@
 	depends on PPC64 && CPU_LITTLE_ENDIAN
 	def_bool !DISABLE_MPROFILE_KERNEL
 
-config IOMMU_HELPER
-	def_bool PPC64
-
 config SWIOTLB
 	bool "SWIOTLB support"
 	default n