vulkan: Implement V7 of ANDROID_native_buffer in nulldrv

Walks the struct chain in GPDP2, and claims support for shared
presentable image. This is enough to have libvulkan expose the
extension for us.

Change-Id: Id22593932cd567e79d18aae788935148d6278b3f
Test: setprop ro.hardware.vulkan default, observe extension exposed