cmake: extensions: Added a new macro zephyr_library_ifdef

Checks if a certain Kconfig is enabled and then do the same
operation as zephyr_library.
If it finds that the Kconfig is not set it will not
create a new library and will stop processing the rest of
the CMakeFile.txt. Usefull in processing the driver Cmake
files.

Signed-off-by: Adithya Baglody <adithya.nagaraj.baglody@intel.com>