kernel: Add rust prebuilts to path

Starting with android common kernel 6.6, rust is enabled for arm64 gki.
It currently looks for rust version 1.73.0, so that was selected as the
default. This was only added for the clang compile path as gki requires
clang.

Change-Id: Ie7b57568d74cfb4a28a94c8dc8f4b5c622044317