x86/mm/dump_pagetables: Add the EFI pagetable to the debugfs 'page_tables' directory

EFI is complicated enough that being able to view its pagetables is
quite helpful.  Rather than requiring users to fish it out of dmesg
on an appropriately configured kernel, let users view it in debugfs
as well.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/ba158a93f3250e6fca752cff2cfb1fcdd9f2b50c.1517414050.git.luto@kernel.org
[ Fixed trivial whitespace damage and fixed missing export. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/platform/efi/efi_64.c

@@ -27,6 +27,7 @@
 #include <linux/ioport.h>
 #include <linux/mc146818rtc.h>
 #include <linux/efi.h>
+#include <linux/export.h>
 #include <linux/uaccess.h>
 #include <linux/io.h>
 #include <linux/reboot.h>
@@ -190,7 +191,8 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
 	early_code_mapping_set_exec(0);
 }
 
-static pgd_t *efi_pgd;
+pgd_t *efi_pgd;
+EXPORT_SYMBOL_GPL(efi_pgd);
 
 /*
  * We need our own copy of the higher levels of the page tables