block: disable multi-page bvec

The multi-page bvec is resulting in the performance regression on
UFS devices in sequential read test for upto ~9%. Hence, disable
it as a workaround.

Change-Id: I1dc3f5e710fd1c9a76f32e3144a0081df755ea26
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>