f_sdp: Change bInterval of interrupt endpoint to 3

Since the USB HID limits the maximum bandwidth(3072) for interrupt
endpoint transfers, when the bInterval set to 1, we can only support 3
boards to run sdp at the same time. In order to support more boards,
change the bInterval of interrupt endpoint to 3, which will not affect
the transmission speed.

Reviewed-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>