usb: gadget: f_gsi: Add support to enable/disable using TCM MEM

This change adds support to enable/disable using TCM memory for
USB IN data buffer with RMNET interface.

Change-Id: I27f04c1bc170e06ccbc9c57ef0e9b8f870e4fe97
Signed-off-by: Mayank Rana <mrana@codeaurora.org>