ACPI / OSI: Add OEM _OSI strings to disable NVidia RTD3

A number of Dell systems require an OEM _OSI string "Linux-Dell-Video"
as a BIOS workaround to disable RTD3 which causes systems hangs when
NVidia graphics cards are installed.  The affected Dell systems are
with system IDs: 0818, 0819, 0820, 0850, 0851, 086F, 0870, 0885 and
0886.

The form of the OEM _OSI strings is defined by each OEMs and is
discussed in Documentation/acpi/osi.txt.

Signed-off-by: Alex Hung <alex.hung@canonical.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/osi.c

@@ -57,6 +57,15 @@ osi_setup_entries[OSI_STRING_ENTRIES_MAX] __initdata = {
 	{"Processor Device", true},
 	{"3.0 _SCP Extensions", true},
 	{"Processor Aggregator Device", true},
+	/*
+	 * Linux-Dell-Video is used by BIOS to disable RTD3 for NVidia graphics
+	 * cards as RTD3 is not supported by drivers now.  Systems with NVidia
+	 * cards will hang without RTD3 disabled.
+	 *
+	 * Once NVidia drivers officially support RTD3, this _OSI strings can
+	 * be removed if both new and old graphics cards are supported.
+	 */
+	{"Linux-Dell-Video", true},
 };
 
 static u32 acpi_osi_handler(acpi_string interface, u32 supported)