mbed: Add enable MCUboot logging parameter and fix logging configuration

This commit add option for a user to enable MCUboot logging from project
configuration level.
Now, logging from MCUboot's sources will be printed in the same way as
mbed-os logs.
Co-created by @AGlass0fMilk - George Beckstein

Signed-off-by: Artur Tynecki <artur.tynecki@mobica.com>
Signed-off-by: George Beckstein <george.beckstein@gmail.com>
diff --git a/boot/mbed/mbed_lib.json b/boot/mbed/mbed_lib.json
index ae8e288..afab39f 100644
--- a/boot/mbed/mbed_lib.json
+++ b/boot/mbed/mbed_lib.json
@@ -64,6 +64,12 @@
             "accepted_values": [true, null],
             "value": null
         },
+        "log-enable": {
+            "help": "Enable MCUboot logging. Must also enable mbed-trace",
+            "macro_name": "MCUBOOT_HAVE_LOGGING",
+            "accepted_values": [true, null],
+            "value": null
+        },
         "log-level": {
             "help": "Verbosity of MCUboot logging.",
             "macro_name": "MCUBOOT_LOG_LEVEL",