fix(build): alias python to 3.8 globally

Internal CI defaults to older versions of Python. In the past we have
used aliases to have access to our minimum required version for building
TF-A. Now that TFTF has the same Python dependencies, this aliasing
needs to happen on a global level.

Change-Id: I989ce5289a9db5098dbde82bb3eb4169c0d50320
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
2 files changed