x86, intel_txt: clean up the impact on generic code, unbreak non-x86

Move tboot.h from asm to linux to fix the build errors of intel_txt
patch on non-X86 platforms. Remove the tboot code from generic code
init/main.c and kernel/cpu.c.

Signed-off-by: Shane Wang <shane.wang@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/reboot.c

@@ -3,6 +3,7 @@
 #include <linux/init.h>
 #include <linux/pm.h>
 #include <linux/efi.h>
+#include <linux/tboot.h>
 #include <acpi/reboot.h>
 #include <asm/io.h>
 #include <asm/apic.h>
@@ -24,8 +25,6 @@
 # include <asm/iommu.h>
 #endif
 
-#include <asm/tboot.h>
-
 /*
  * Power off function, if any
  */