drm/i915/guc: don't hardcode BCS0 in guc_hang selftest

On MTL there are no BCS engines on the media GT, so we can't always use
BCS0 in the test. There is no actual reason to use a BCS engine over an
engine of a different class, so switch to using any available engine.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Acked-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221102214310.2829310-1-daniele.ceraolospurio@intel.com