vulkan: Allow AHB extension to get to the driver

We don't need to do anything special with the AHB extension at the
driver layer, but it's defined as a "known extension" so that we can
export symbols for it. So it didn't fall into the generic extension
path, but we also didn't add it to the list to pass on to the driver.
So drivers were never seeing that the extension was enabled.

Remove switch default cases, so that -Wswitch can catch bugs like this
in the future.

Test: in-progress MediaVulkanGpuTest (ag/3789901/18)
Bug: 77297007
Change-Id: I3fe460240cfd1f868b7275abbb0289b806bc7603