x86: Make Dell Latitude E6420 use reboot=pci

Yet another variant of the Dell Latitude series which requires
reboot=pci.

From the E5420 bug report by Daniel J Blueman:

> The E6420 is affected also (same platform, different casing and
> features), which provides an external confirmation of the issue; I can
> submit a patch for that later or include it if you prefer:
> http://linux.koolsolutions.com/2009/08/04/howto-fix-linux-hangfreeze-during-reboots-and-restarts/Reported-by: NDaniel J Blueman <daniel.blueman@gmail.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>
Cc: <stable@kernel.org>

arch/x86/kernel/reboot.c

@@ -435,6 +435,14 @@ static struct dmi_system_id __initdata pci_reboot_dmi_table[] = {
 			DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E5420"),
 		},
 	},
+	{	/* Handle problems with rebooting on the Latitude E6420. */
+		.callback = set_pci_reboot,
+		.ident = "Dell Latitude E6420",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
+			DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E6420"),
+		},
+	},
 	{ }
 };