vulkan: Tolerate missing GetSwapchainGrallocUsageANDROID function

Some drivers implementing ANDROID_native_buffer V6 have /removed/ the
old function. We shouldn't really mind if they do that -- we're never
going to call it anyway if they do expose the new
GetSwapchainGrallocUsage2ANDROID function.

V2: Fail at CreateDevice-time if neither function is exposed.

Change-Id: Id1e3dd5e2e71a9291dd610e908f9906acaaf0ad0
Related bugs: b/34177594
Test: build