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/arch/i386/mach-generic/bigsmp.c b/arch/i386/mach-generic/bigsmp.c
index 58a477b..292a225 100644
--- a/arch/i386/mach-generic/bigsmp.c
+++ b/arch/i386/mach-generic/bigsmp.c
@@ -21,7 +21,7 @@
 
 static int dmi_bigsmp; /* can be set by dmi scanners */
 
-static int hp_ht_bigsmp(struct dmi_system_id *d)
+static int hp_ht_bigsmp(const struct dmi_system_id *d)
 {
 #ifdef CONFIG_X86_GENERICARCH
 	printk(KERN_NOTICE "%s detected: force use of apic=bigsmp\n", d->ident);
@@ -31,7 +31,7 @@
 }
 
 
-static struct dmi_system_id bigsmp_dmi_table[] = {
+static const struct dmi_system_id bigsmp_dmi_table[] = {
 	{ hp_ht_bigsmp, "HP ProLiant DL760 G2", {
 		DMI_MATCH(DMI_BIOS_VENDOR, "HP"),
 		DMI_MATCH(DMI_BIOS_VERSION, "P44-"),