x86, 64bit, realmode: Use init_level4_pgt to set trampoline_pgd directly

with #PF handler way to set early page table, level3_ident will go away with
64bit native path.

So just use entries in init_level4_pgt to set them in trampoline_pgd.
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1359058816-7615-10-git-send-email-yinghai@kernel.org
Cc: Jarkko Sakkinen <jarkko.sakkinen@intel.com>
Acked-by: Jarkko Sakkinen <jarkko.sakkinen@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/realmode/init.c

@@ -78,8 +78,8 @@ void __init setup_real_mode(void)
 	*trampoline_cr4_features = read_cr4();
 
 	trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd);
-	trampoline_pgd[0] = __pa(level3_ident_pgt) + _KERNPG_TABLE;
-	trampoline_pgd[511] = __pa(level3_kernel_pgt) + _KERNPG_TABLE;
+	trampoline_pgd[0] = init_level4_pgt[pgd_index(__PAGE_OFFSET)].pgd;
+	trampoline_pgd[511] = init_level4_pgt[511].pgd;
 #endif
 }