vulkan: rework DriverDispatchTable

Generate {Instance,Device}DriverTable from code-generator.tmpl to replace
dispatch.tmpl entirely.  The new code avoids initializing
VK_ANDROID_native_buffer entries when the extension is not enabled.  The
separation of instance and device driver tables also allows us to
initialize the device driver table with vkGetDeviceProcAddr, which is
expected to return more efficient function pointers on properly
implemented HALs.

CreateInstance_Bottom always has a potential resource leak when the
HAL-created instance does not contain HWVULKAN_DISPATCH_MAGIC.
CreateDevice_Bottom now has the same issue.  Both of them will be fixed in
following commits.

Change-Id: If7800ef23098121f1fff643a2c5224c2c9be0711