samsung-laptop: Disable on EFI hardware

It has been reported that running this driver on some Samsung laptops
with EFI can cause those machines to become bricked as detailed in the
following report,

	https://bugs.launchpad.net/ubuntu-cdimage/+bug/1040557

There have also been reports of this driver causing Machine Check
Exceptions on recent EFI-enabled Samsung laptops,

	https://bugzilla.kernel.org/show_bug.cgi?id=47121

So disable it if booting from EFI since this driver relies on
grovelling around in the BIOS memory map which isn't going to work.

Cc: Corentin Chary <corentincj@iksaif.net>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Steve Langasek <steve.langasek@canonical.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

drivers/platform/x86/samsung-laptop.c

@@ -26,6 +26,7 @@
 #include <linux/seq_file.h>
 #include <linux/debugfs.h>
 #include <linux/ctype.h>
+#include <linux/efi.h>
 #include <acpi/video.h>
 
 /*
@@ -1544,6 +1545,9 @@ static int __init samsung_init(void)
 	struct samsung_laptop *samsung;
 	int ret;
 
+	if (efi_enabled(EFI_BOOT))
+		return -ENODEV;
+
 	quirks = &samsung_unknown;
 	if (!force && !dmi_check_system(samsung_dmi_table))
 		return -ENODEV;