tuna: increase hispeed_freq to 920 mhz

Change-Id: Iecbc07f26a7c8efe589e6d8f8216a14c55ffccc9
tuna: tune lowmemorykiller for 1gb ram

Cherry-picked from fugu.

Change-Id: Id7ea084fbf90d45a0ab81b1566b9ce6a9867fd19