drivers/firmware: const-ify DMI API and internals

Three main sets of changes:

1) dmi_get_system_info() return value should have been marked const,
   since callers should not be changing that data.

2) const-ify DMI internals, since DMI firmware tables should,
   whenever possible, be marked const to ensure we never ever write to
   that data area.

3) const-ify DMI API, to enable marking tables const where possible
   in low-level drivers.

And if we're really lucky, this might enable some additional
optimizations on the part of the compiler.

The bulk of the changes are #2 and #3, which are interrelated.  #1 could
have been a separate patch, but it was so small compared to the others,
it was easier to roll it into this changeset.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
diff --git a/drivers/hwmon/hdaps.c b/drivers/hwmon/hdaps.c
index e0cf5e6..a7c6d40 100644
--- a/drivers/hwmon/hdaps.c
+++ b/drivers/hwmon/hdaps.c
@@ -480,14 +480,14 @@
 /* Module stuff */
 
 /* hdaps_dmi_match - found a match.  return one, short-circuiting the hunt. */
-static int __init hdaps_dmi_match(struct dmi_system_id *id)
+static int __init hdaps_dmi_match(const struct dmi_system_id *id)
 {
 	printk(KERN_INFO "hdaps: %s detected.\n", id->ident);
 	return 1;
 }
 
 /* hdaps_dmi_match_invert - found an inverted match. */
-static int __init hdaps_dmi_match_invert(struct dmi_system_id *id)
+static int __init hdaps_dmi_match_invert(const struct dmi_system_id *id)
 {
 	hdaps_invert = 1;
 	printk(KERN_INFO "hdaps: inverting axis readings.\n");