Fix recent apps in system UI for Skia pipeline

Enable HW Bitmaps for Skia pipeline just enough to make
recent apps list working by adding support for BitmapShader.
Drawing HW bitmaps in a canvas is also supported.

Test: recent apps work, HWUI unit tests pass, CTS tests pass.
bug: 38136140
Change-Id: Ibd06c859c86dc213310d5ce5272497e1882d0cc6