drm/xe: Return forcewake reference type from force_wake_get_any_engine()

drm/xe: Return forcewake reference type from force_wake_get_any_engine()

Adjust the signature of force_wake_get_any_engine() such that it returns
a 'struct xe_force_wake_ref' rather than a boolean success/failure.
Failure cases are now recognized by inspecting the hardware engine
returned by reference; a NULL hwe indicates that no engine's forcewake
could be obtained.

These changes will make it cleaner and easier to incorporate scope-based
cleanup in force_wake_get_any_engine()'s caller in a future patch.

Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patch.msgid.link/20251118164338.3572146-43-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>