mm: don't throttle ULMK on direct reclaim

A very low on memory condition causes all the processes entering in the
direct reclaim are forced to throttle. This forces the system to hung
until any single process, usually kthreads other than kswapd, in the
system to enter direct reclaim thus get help from
should_ulmk_retry()->out_of_memory(adj >= 0). Worse is the case where
ULMK also gets throttled. With out relying on kthreads, make a way for
ULMK to enter direct reclaim by bypassing throttle_direct_reclaim().

Change-Id: I48c0d32b6617db9914b97825631e8c93bdf2e4a1
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>