Enable GIT_SHALLOW and GIT_PROGRESS

Use git shallow cloning to try and speed up the CMake configure stage.
Unfortunately FetchContent does not support the git --shallow-submodules
option at present, so cloning the ML Evaluation Kit in particular takes
a long time, as it has several large submodule dependencies.

This change still seems to improve the configure time by 20 seconds on a
2018 Macbook Pro with 100mbps download speed.

Also enable the GIT_PROGRESS option so clone progress can be viewed in
the terminal when FETCHCONTENT_QUIET is set to OFF by the user.

Signed-off-by: Robert Walton <rob.walton@arm.com>