[TF-M] Support for optional build for secure partitions and test suites

Hi,

I've made some patches to support optional build for secure partitions and test suites: https://review.trustedfirmware.org/q/topic:%22optional_build_sp_and_tests%22...)

With this patch set, you can optionally build secure partitions by setting the TFM_PARTITION_XXX in CommonConfig.cmake around line 152 - 162. And for test suites, by setting ENABLE_XXX_TESTS in test/TestConfig.cmake.

I'm collecting for review comments. Thanks.

Best Regards, Kevin