USB: gadget: u_data_ipa: Handle usb requests allocation/free correctly

Currently USB requests are allocated during connect work for starting
endless TX and RX in BAM2BAM over IPA. But these requests are not freed
during disconnect which leads to memory leak and could result in memory
allocation failure in function drivers during next connect. Hence free USB
requests allocated during disconnect to fix memleak issue and also move
allocation of RX/TX usb requests to gbam_connect to avoid crashes due
to NULL pointer dereference.

Also extend spinlock protection to avoid the crashes during connect and
disconnect functions.

Change-Id: I4362fde2928857253d2150e4d9531cada876cd58
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>