drm/xe: Convert kunit tests from mem_access to xe_pm_runtime

Let's convert the kunit tests that are currently relying on
xe_device_mem_access_{get,put} towards the direct xe_pm_runtime_{get,put}.
While doing this we need to move the get/put calls towards the outer
bounds of the tests to ensure consistency with the other usages of
pm_runtime on the regular paths.

v2: include xe_pm.h in tests/xe_mocs.c and sort the include block
    while at it.

Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240222163937.138342-4-rodrigo.vivi@intel.com