soundwire: cadence_master: check the number of bidir PDIs

There is an assumption that the first two PDIs are reserved for Bulk,
so we need to make sure the number of bidir PDIs is indeed larger than
two. If the configuration provided is incorrect, this could lead to
allocating a huge amount of memory.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>