This CL defines minui_backend as an interface, and expresses the three
backends (adf, drm and fbdev) as subclasses to the interface.
Test: 'Run graphics test' on N9, Pixel C and N5X.
Change-Id: I0e23951c7b2e2ff918957a8d9fc8b0085b6e5952
Remove unneeded header includes. Switch a few memset() to '= {}'
style. Otherwise mostly cosmetic changes like reformatting.
Test: 'Run graphics test' on ryu (which is a DRM device).
Change-Id: I4b0ab2dc0da69a690f09e4f0674b8377de662962
