accel/habanalabs: fix register address on PDMA/EDMA idle check

The PDMA/EDMA is_idle routines didn't check the correct CORE register
in order to get the accurate idle state.
Moreover, it's better to make the is_idle routine more robust by adding
additional checks (IS_HALTED) before announcing that the core is idle.

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