Fetch ML evaluation kit using CMake FetchContent

Note:
When we call FetchContent_MakeAvailable in Cmake it fetches the
content and calls CMake of ml-embedded-evaluation-kit complaints
about the missing compiler configuration so replace it with
FetchContent_Populate to fetches ml-embedded-evaluation-kit sources alone

Signed-off-by: Rajkumar Kanagaraj <rajkumar.kanagaraj@arm.com>