Fix mismatch between isSupported & allocate

isSupported failed to validate usage bits like allocate does,
meaning that isSupported can return true if a vendor is unaware
of a usage bit but then allocate will (correctly!) fail to allocate.

Fix this so that all buffer descriptions go through the same
validation path.

Bug: 216478685
Test: atest HardwareBufferTest#testInvalidUsage
Change-Id: Idc9a0837f555beceb604f27a06e4833f41e97261