mk: config.mk: describe CFG_WITH_STATS

Adds a description for CFG_WITH_STATS and explicitly states that the
config switch is default disabled.

Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>

mk/config.mk

@@ -553,6 +553,10 @@ CFG_DRIVERS_CLK_EARLY_PROBE ?= n
 $(call force,CFG_DRIVERS_DT_RECURSIVE_PROBE,n,Mandated by CFG_DT_DRIVER_EMBEDDED_TEST)
 endif
 
+# CFG_WITH_STATS when enabled embeds PTA statistics service to allow non-secure
+# clients to retrieve debug and statistics information on core and loaded TAs.
+CFG_WITH_STATS ?= n
+
 # CFG_DRIVERS_DT_RECURSIVE_PROBE when enabled forces a recursive subnode
 # parsing in the embedded DTB for driver probing. The alternative is
 # an exploration based on compatible drivers found. It is default disabled.