It is impossible to disable BQL individually today, since there is no
prompt for the Kconfig entry, so, the BQL is always enabled if SYSFS is
enabled.

Create a prompt entry for BQL, so, it could be enabled or disabled at
build time independently of SYSFS.
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: David S. Miller <davem@davemloft.net>