drm/xe/tests: Set non-GMDID graphics step in xe_pci_fake_device_init()

drm/xe/tests: Set non-GMDID graphics step in xe_pci_fake_device_init()

Currently the logic to set the graphics step for non-GMDID-based
platforms in kunit testing is defined in xe_wa_test_init().  That
logic should rather belong to the helper xe_pci_fake_device_init(), so
move it there.

Reviewed-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
Reviewed-by: Violet Monti <violet.monti@intel.com>
Link: https://patch.msgid.link/20260609-xe-probe-info-v1-6-21e83e188e60@intel.com
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>