board: updating test cases for intel s1000 crb board

Changing ZEPHYR_BASE throughout Zephyr tests and samples revealed that
intel s1000 crb cache test case could not be run on CI.

This has now been fixed by moving the tests file located in
tests/board/intel_s1000_crb folder into tests/board/intel_s1000_crb/main
instead so there is now main and cache folders with test projects.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>