usb: u_bam: Support new event to update RX buffer size

Add support for a new event BAM_DMUX_TRANSMIT_SIZE to update
Rx Buffer size when received this event from BAM DMUX side.
The event is triggered every time when msm_bam_dmux_open
function is called. The skb buffer allocation will be done
in gbam_start_io function after msm_bam_dmux_open function.
This new event support will allow to send larger data payloads.

CRs-Fixed: 658306
Change-Id: I01cb1f43f7b745e58645c3b7a3b344e544feff0b
Signed-off-by: Guang Jian Zeng <gzeng@codeaurora.org>
Signed-off-by: Sujeet Kumar <ksujeet@codeaurora.org>