[MIPS] R4000/R4400 errata workarounds

This is the gereric part of R4000/R4400 errata workarounds.  They include 
compiler and assembler support as well as some source code modifications 
to address the problems with some combinations of multiply/divide+shift 
instructions as well as the daddi and daddiu instructions.

 Changes included are as follows:

1. New Kconfig options to select workarounds by platforms as necessary.

2. Arch top-level Makefile to pass necessary options to the compiler; also 
   incompatible configurations are detected (-mno-sym32 unsupported as 
   horribly intrusive for little gain).

3. Bug detection updated and shuffled -- the multiply/divide+shift problem 
   is lethal enough that if not worked around it makes the kernel crash in 
   time_init() because of a division by zero; the daddiu erratum might 
   also trigger early potentially, though I have not observed it.  On the 
   other hand the daddi detection code requires the exception subsystem to 
   have been initialised (and is there mainly for information).

4. r4k_daddiu_bug() added so that the existence of the erratum can be 
   queried by code at the run time as necessary; useful for generated code 
   like TLB fault and copy/clear page handlers.

5. __udelay() updated as it uses multiplication in inline assembly.

 Note that -mdaddi requires modified toolchain (which has been maintained 
by myself and available from my site for ~4years now -- versions covered 
are GCC 2.95.4 - 4.1.2 and binutils from 2.13 onwards).  The -mfix-r4000 
and -mfix-r4400 have been standard for a while though.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/setup.c

@@ -8,7 +8,7 @@
  * Copyright (C) 1994, 95, 96, 97, 98, 99, 2000, 01, 02, 03  Ralf Baechle
  * Copyright (C) 1996 Stoned Elipot
  * Copyright (C) 1999 Silicon Graphics, Inc.
- * Copyright (C) 2000 2001, 2002  Maciej W. Rozycki
+ * Copyright (C) 2000, 2001, 2002, 2007  Maciej W. Rozycki
  */
 #include <linux/init.h>
 #include <linux/ioport.h>
@@ -24,6 +24,7 @@
 
 #include <asm/addrspace.h>
 #include <asm/bootinfo.h>
+#include <asm/bugs.h>
 #include <asm/cache.h>
 #include <asm/cpu.h>
 #include <asm/sections.h>
@@ -561,6 +562,7 @@ void __init setup_arch(char **cmdline_p)
 	}
 #endif
 	cpu_report();
+	check_bugs_early();
 
 #if defined(CONFIG_VT)
 #if defined(CONFIG_VGA_CONSOLE)