lib: os: CONFIG_HEAP_LISTENER to be hidden
lib: os: CONFIG_HEAP_LISTENER to be hidden

This changes CONFIG_HEAP_LISTENER to be a hidden kconfig so that
the actual heap implementation can select it to enable
notifications. Each heap implementations will have their own
kconfigs to enable heap listener functionality so that app
can be built to only listen to certain heap implementations.

Signed-off-by: Daniel Leung <d94e04d205b5962d7873a139ef298b03c1717f72@intel.com>

finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr