lib: notify: build sys-notify conditionally.

Add a new Kconfig and build this code conditionally, so we do not end up
with this file being built for each zephyr app.

Partial fix for #50654

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

drivers/counter/Kconfig.maxim_ds3231

@@ -9,5 +9,6 @@ config COUNTER_MAXIM_DS3231
 	depends on DT_HAS_MAXIM_DS3231_ENABLED
 	depends on I2C
 	select POLL
+	select NOTIFY
 	help
 	  Enable counter driver based on Maxim DS3231 I2C device.

lib/os/CMakeLists.txt

@@ -12,7 +12,6 @@ zephyr_sources(
   dec.c
   fdtable.c
   hex.c
-  notify.c
   printk.c
   rb.c
   sem.c
@@ -25,6 +24,7 @@ zephyr_sources(
   )
 
 zephyr_sources_ifdef(CONFIG_ONOFF onoff.c)
+zephyr_sources_ifdef(CONFIG_NOTIFY notify.c)
 
 zephyr_sources_ifdef(CONFIG_CBPRINTF_COMPLETE cbprintf_complete.c)
 zephyr_sources_ifdef(CONFIG_CBPRINTF_NANO cbprintf_nano.c)

lib/os/Kconfig

@@ -16,6 +16,11 @@ config RING_BUFFER
 	  buffers manage their own buffer memory and can store arbitrary data.
 	  For optimal performance, use buffer sizes that are a power of 2.
 
+config NOTIFY
+	bool "Asynchronous Notifications"
+	help
+	  Use this API to support async transactions.
+
 config BASE64
 	bool "Base64 encoding and decoding"
 	help
@@ -40,6 +45,7 @@ config MPSC_PBUF
 
 config ONOFF
 	bool "On-Off Manager"
+	select NOTIFY
 	help
 	  An on-off manager supports an arbitrary number of clients of a
 	  service which has a binary state.  Example applications are power

tests/lib/notify/prj.conf

@@ -1,3 +1,4 @@
 CONFIG_POLL=y
 CONFIG_ZTEST=y
 CONFIG_ZTEST_NEW_API=y
+CONFIG_NOTIFY=y