diag: Remove AXI prefetch related padding

Currently, diag is adding padding of 256 bytes as
a workaround to get rid of AXI prefetch related h/w
issue while writing data to USB. The patch removes
the padding wherever h/w issue is not applicable to
optimize memory allocation.

CRs-Fixed: 2123113
Change-Id: Ia5b2eec1b2fb5bc5b15a572c68ee4da3ce97a19c
Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>