usb: bam: ZLT issue workaround

IPA sends ZLT when using aggregation, and USB3.0 DBM is not able
to handle properly those ZLT for all cases.

Therefore, we need to eliminate ZLT on USB side by using max threshold
in BAM, so that the USB bam will get notifications only when EOT flag
is set in the descriptor FIFO.

Change-Id: I5866d755fa34eeaab51ad7fe5f9a8b2006bbc5fe
Signed-off-by: Bar Weiner <bweiner@codeaurora.org>