diag: diag over uart not working for QSC

On executing diag_uart_log app with QSC option
switching is not happening. On the other hand, MSM
switching is working fine. Added changes in order
to allocate memory to user space data type buffer
during diag char initialization.

Change-Id: I8afd79017e543b088381fd70c2a585f6c0c2ca1e
CRs-Fixed: 576830
Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>