accel/habanalabs: remove a useless is_idle TPC flag

Is appears that the flag -
DCORE0_TPC0_CFG_STATUS_VECTOR_PIPE_EMPTY_MASK, has no actual use when
it comes to querying TPC idleness, since this flag's corresponding bit
turns-off after stalling the engine, and turns back on after resuming
it.

Signed-off-by: Koby Elbaz <kelbaz@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>