[nrf toup][nrfconnect] Enable LTO for all-clusters-app on nRF52840 dongle

Enablue LTO for dongle due to flash overflow.

Signed-off-by: Adrian Gielniewski <[email protected]>

Author: adigie

examples/all-clusters-app/nrfconnect/boards/nrf52840dongle_nrf52840.conf

@@ -35,3 +35,7 @@ CONFIG_ASSERT_VERBOSE=n
 CONFIG_SHELL=n
 CONFIG_OPENTHREAD_SHELL=n
 CONFIG_MATTER_LOG_LEVEL_INF=y
+
+# Enable LTO to reduce the flash usage
+CONFIG_LTO=y
+CONFIG_ISR_TABLES_LOCAL_DECLARATION=y