ACPI, APEI, GHES, Support disable GHES at boot time

Some machine may have broken firmware so that GHES and firmware first
mode should be disabled.  This patch adds support to that.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/include/acpi/apei.h b/include/acpi/apei.h
index e67b523..d40bc55 100644
--- a/include/acpi/apei.h
+++ b/include/acpi/apei.h
@@ -18,6 +18,7 @@
 
 extern int hest_disable;
 extern int erst_disable;
+extern int ghes_disable;
 
 #ifdef CONFIG_ACPI_APEI
 void __init acpi_hest_init(void);