Refactor build template for aarch64.
Refactor build template for aarch64.

Add a new toolchain variation for clang with bfd linker.

Change-Id: Ied16f22c1b0e8e49420684029df8020a00a13a57

project-oak/hafnium-verification,project-oak/hafnium-verification,project-oak/hafnium-verification,project-oak/hafnium-verification,project-oak/hafnium-verification,project-oak/hafnium-verification,project-oak/hafnium-verification