Forward extra defines from the aarch64_common_toolchain.
Forward extra defines from the aarch64_common_toolchain.

Extra defines can now be added to aarch64_toolchain templates.

Change-Id: Ib83519099a1b05083c4e1c27c6bd235af1be3430

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