graphics: improve preloading for IMapper default impl

When GraphicBufferMapper::preloadHal dlopens the default impl, make sure
the gralloc module is also dlopen'ed.

Bug: 269664560
Test: android.view.cts.PixelCopyTest#testVideoProducer on grunt

Change-Id: I57418338d5212fb9a2c1ea82eba63d855f69ff32
2 files changed