x86/boot: Obsolete the MCA sys_desc_table

The kernel does not support the MCA bus anymroe, so mark sys_desc_table
as obsolete: remove any reference from the code together with the remaining
of MCA logic.

bloat-o-meter output:

  add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-55 (-55)
  function                                     old     new   delta
  i386_start_kernel                            128     119      -9
  setup_arch                                  1421    1375     -46

Signed-off-by: Paolo Pisati <p.pisati@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1437409430-8491-1-git-send-email-p.pisati@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/Documentation/x86/zero-page.txt b/Documentation/x86/zero-page.txt
index 82fbdbc..95a4d34 100644
--- a/Documentation/x86/zero-page.txt
+++ b/Documentation/x86/zero-page.txt
@@ -17,7 +17,8 @@
 				(struct ist_info)
 080/010	ALL	hd0_info	hd0 disk parameter, OBSOLETE!!
 090/010	ALL	hd1_info	hd1 disk parameter, OBSOLETE!!
-0A0/010	ALL	sys_desc_table	System description table (struct sys_desc_table)
+0A0/010	ALL	sys_desc_table	System description table (struct sys_desc_table),
+				OBSOLETE!!
 0B0/010	ALL	olpc_ofw_header	OLPC's OpenFirmware CIF and friends
 0C0/004	ALL	ext_ramdisk_image ramdisk_image high 32bits
 0C4/004	ALL	ext_ramdisk_size  ramdisk_size high 32bits