efi/reboot: Add generic wrapper around EfiResetSystem()

Implement efi_reboot(), which is really just a wrapper around the
EfiResetSystem() EFI runtime service, but it does at least allow us to
funnel all callers through a single location.

It also simplifies the callsites since users no longer need to check to
see whether EFI_RUNTIME_SERVICES are enabled.

Cc: Tony Luck <tony.luck@intel.com>
Tested-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 3a64f2f..e6980ba 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -20,6 +20,7 @@
 #include <linux/ioport.h>
 #include <linux/pfn.h>
 #include <linux/pstore.h>
+#include <linux/reboot.h>
 
 #include <asm/page.h>
 
@@ -928,11 +929,14 @@
 {
 	return test_bit(feature, &efi.flags) != 0;
 }
+extern void efi_reboot(enum reboot_mode reboot_mode, const char *__unused);
 #else
 static inline bool efi_enabled(int feature)
 {
 	return false;
 }
+static inline void
+efi_reboot(enum reboot_mode reboot_mode, const char *__unused) {}
 #endif
 
 /*