Recycle the bitmap as soon as possible

Recycle the bitmap as soon as possible to release native heap.
According to meminfo, it uses around 20MB less than the version
which waits for gc.

Bug: 149744069
Bug: 147379974
Test: mp sysuig and reboot to lockscreen
Test: adb shell dumpsys meminfo com.android.systemui
Change-Id: I513edc62b868e6c9a6a3e3b7420961acc606eb0f