Add the Arm GNU 9.2 Binary Toolchain

Add the Arm GNU Binary Toolchain as a third party prebuilt.
This is needed for the aarch64 cross compiler (gcc), to
facilitate CI testing.

Signed-off-by: Fuad Tabba <tabba@google.com>
Change-Id: I3b942f86108d17d95a239f235a5c0bc37d01d588