habanalabs: don't limit packet size for device CPU

This patch removes a limitation on the maximum packet size that is read by
the device CPU as that limitation is not needed.

Therefore, the patch also removes an elaborate calculation that is based
on this limitation which is also not needed now. Instead, use a fixed
value for the memory pool size of the packets.

Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>