components: Make DeclareSdkComponents a module

Make DeclareSdkComponents a module, so that we can declare the
components earlier in the build process. This allows us to have
components declared before adding some tests that are added before
components (like those in the utils/tests directory). An additional
benefit is that other projects can easily fetch the same "tested and
proven" versions of components that the SDK ships with, even if it
doesn't use anything else from the SDK.

Signed-off-by: Jaeden Amero <jaeden.amero@arm.com>
Signed-off-by: Filip Jagodzinski <filip.jagodzinski@arm.com>