USB: u_bam: Copy data to host in work queue context

Currently data to host is being sent in interrupt context
instead of work queue context which might hit perforamce.
Hence move this processing to work queue context.

With standalone dataloopback test, increments in throughput numbers
are observed as follows(Mbps):
TCP uplink	29.7	53.1
TCP downlink	29.8	53.7
UDP uplink	16.7	22.7
UDP downlink	20.8	24.2

Change-Id: I72ae2ccb0aee43db5a69514a002eba78ae647573
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>