drm/xe/tests: Add helpers for use in live tests

Instead of iterating over available Xe devices within a testcase,
without being able to distinguish potential failures from different
devices on system with many Xe devices, introduce helpers that will
allow to treat each Xe device as a parameter for the testcase like:

static void bar(struct kunit *test)
{
	struct xe_device *xe = test->priv;
	...
}

struct kunit_case foo_live_tests[] = {
	KUNIT_CASE_PARAM(bar, xe_pci_live_device_gen_param),
	{}
};

struct kunit_suite foo_suite = {
	.name = "foo_live",
	.test_cases = foo_live_tests,
	.init = xe_kunit_helper_xe_device_live_test_init,
};

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240720142528.530-3-michal.wajdeczko@intel.com