drm/vkms: Update testing with IGT IGT_DEVICE

VKMS is no longer in the platform bus, instead, it is in the faux bus.

In addition, when present, IGT picks hardware drivers instead of virtual
drivers, like VKMS or vgem, if they are not forced.

Update the documentation to use IGT_FORCE_DRIVER instead of IGT_DEVICE.

Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Link: https://lore.kernel.org/r/20251024110014.4614-2-jose.exposito89@gmail.com
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>

Author: JoseExposito

Documentation/gpu/vkms.rst

@@ -159,26 +159,23 @@ To return to graphical mode, do::
 
   sudo systemctl isolate graphical.target
 
-Once you are in text only mode, you can run tests using the --device switch
-or IGT_DEVICE variable to specify the device filter for the driver we want
-to test. IGT_DEVICE can also be used with the run-tests.sh script to run the
+Once you are in text only mode, you can run tests using the IGT_FORCE_DRIVER
+variable to specify the device filter for the driver we want to test.
+IGT_FORCE_DRIVER can also be used with the run-tests.sh script to run the
 tests for a specific driver::
 
-  sudo ./build/tests/<name of test> --device "sys:/sys/devices/platform/vkms"
-  sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/<name of test>
-  sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./scripts/run-tests.sh -t <name of test>
+  sudo IGT_FORCE_DRIVER="vkms" ./build/tests/<name of test>
+  sudo IGT_FORCE_DRIVER="vkms" ./scripts/run-tests.sh -t <name of test>
 
 For example, to test the functionality of the writeback library,
 we can run the kms_writeback test::
 
-  sudo ./build/tests/kms_writeback --device "sys:/sys/devices/platform/vkms"
-  sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/kms_writeback
-  sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./scripts/run-tests.sh -t kms_writeback
+  sudo IGT_FORCE_DRIVER="vkms" ./build/tests/kms_writeback
+  sudo IGT_FORCE_DRIVER="vkms" ./scripts/run-tests.sh -t kms_writeback
 
 You can also run subtests if you do not want to run the entire test::
 
-  sudo ./build/tests/kms_flip --run-subtest basic-plain-flip --device "sys:/sys/devices/platform/vkms"
-  sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/kms_flip --run-subtest basic-plain-flip
+  sudo IGT_FORCE_DRIVER="vkms" ./build/tests/kms_flip --run-subtest basic-plain-flip
 
 Testing With KUnit
 ==================