x86 boot: add header comment to dmi.h stating what it is

The "dmi.h" file did not state anywhere in the file what "DMI" was.
For those who know, it's obvious.  For the rest of us, I added a
brief opening comment.
Signed-off-by: NPaul Jackson <pj@sgi.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

drivers/firmware/dmi_scan.c

@@ -8,6 +8,11 @@
 #include <linux/slab.h>
 #include <asm/dmi.h>
 
+/*
+ * DMI stands for "Desktop Management Interface".  It is part
+ * of and an antecedent to, SMBIOS, which stands for System
+ * Management BIOS.  See further: http://www.dmtf.org/standards
+ */
 static char dmi_empty_string[] = "        ";
 
 static const char * __init dmi_string_nosave(const struct dmi_header *dm, u8 s)