x86: Use x86_platform for iommu_shutdown

This patch cleans up pci_iommu_shutdown() a bit to use
x86_platform (similar to how IA64 initializes an IOMMU driver).

This adds iommu_shutdown() to x86_platform to avoid calling
every IOMMUs' shutdown functions in pci_iommu_shutdown() in
order. The IOMMU shutdown functions are platform specific (we
don't have multiple different IOMMU hardware) so the current way
is pointless.

An IOMMU driver sets x86_platform.iommu_shutdown to the shutdown
function if necessary.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: joerg.roedel@amd.com
LKML-Reference: <20091027163358F.fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index f930787..2b97fc5 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -23,7 +23,7 @@
 # include <linux/ctype.h>
 # include <linux/mc146818rtc.h>
 #else
-# include <asm/iommu.h>
+# include <asm/x86_init.h>
 #endif
 
 /*
@@ -622,7 +622,7 @@
 #endif
 
 #ifdef CONFIG_X86_64
-	pci_iommu_shutdown();
+	x86_platform.iommu_shutdown();
 #endif
 }