usb: gadget: f_gsi: Add module param to change the OUT aggregation

Add module param to change the OUT aggregation size.
Module param can be updated as

echo 10240 > /sys/module/g_android/parameters/gsi_out_aggr_size

Also add macros for the out request buffer length values for each
protocol.

Change-Id: Ib8952ed6c5c1c6d8c47a0a7afc62010580666f74
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>