Revert "x86_64: there's no need to preallocate level1_fixmap_pgt"

This reverts commit 033786969d1d1b5af12a32a19d3a760314d05329.

Suresh Siddha reported that this broke booting on his 2GB testbox.
Reported-by: NSuresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/head_64.S

@@ -362,6 +362,12 @@ NEXT_PAGE(level3_kernel_pgt)
 	.quad	level2_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
 
 NEXT_PAGE(level2_fixmap_pgt)
+	.fill	506,8,0
+	.quad	level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
+	/* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
+	.fill	5,8,0
+
+NEXT_PAGE(level1_fixmap_pgt)
 	.fill	512,8,0
 
 NEXT_PAGE(level2_ident_pgt)