accel/habanalabs: remove unused asic functions

asic_dma_{un}map_single() asic-specific functions are no longer called
from the common code, so delete these functions.

In addition, delete the gaudi2 implementation as they are also not
called.

Signed-off-by: Oded Gabbay <ogabbay@kernel.org>
Reviewed-by: Ofir Bitton <obitton@habana.ai>