cmake: Move the invocation of 'project' earlier

The CMake documentation for 'project' states "Call the project()
command near the top of the top-level CMakeLists.txt". Meaning, it
should be run as early as possible.

An obscure internal error was observed when 'project' was located in
zephyr/CMakeLists.txt and was observed to be fixed after moving
'project' earlier, hence this patch that moves it earlier.

Invoking project depends on knowing information about the toolchain so
it is placed after target_toolchain.cmake.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>