ACPI: make blacklist more verbose

IMHO, ACPI disabled due to DMI failure or blacklisted year should be noted,
as is done with other ACPI blacklisting.

This will help people troubleshoot when ACPI isn't working.  Status quo is
a mysterious "ACPI Disabled" message without explanation on BIOS that
implements ACPI but not DMI.  This is actually fairly common on embedded
x86 boards.
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLen Brown <len.brown@intel.com>

drivers/acpi/blacklist.c

@@ -79,11 +79,17 @@ static int __init blacklist_by_year(void)
 {
 	int year = dmi_get_year(DMI_BIOS_DATE);
 	/* Doesn't exist? Likely an old system */
-	if (year == -1)
+	if (year == -1) {
+		printk(KERN_ERR PREFIX "no DMI BIOS year, "
+			"acpi=force is required to enable ACPI\n" );
 		return 1;
+	}
 	/* 0? Likely a buggy new BIOS */
-	if (year == 0)
+	if (year == 0) {
+		printk(KERN_ERR PREFIX "DMI BIOS year==0, "
+			"assuming ACPI-capable machine\n" );
 		return 0;
+	}
 	if (year < CONFIG_ACPI_BLACKLIST_YEAR) {
 		printk(KERN_ERR PREFIX "BIOS age (%d) fails cutoff (%d), "
 		       "acpi=force is required to enable ACPI\n",