Updated mbed_app.json5 with tested working configuration for DISCO_F746NG

Author: zhiyong-ft

mbed_app.json5

@@ -51,7 +51,16 @@
         //     "mcuboot.read-granularity": 1,
         //     "qspif.QSPI_MIN_PROG_SIZE": 1
         // },
-
+        "DISCO_F746NG": {
+            "target.restrict_size": "0x18000",
+            "mcuboot.primary-slot-address": "0x8018000",
+            "mcuboot.slot-size": "0xA8000",
+            "mcuboot.scratch-address": "0x80C0000",
+            "mcuboot.scratch-size": "0x40000",
+            "mcuboot.max-img-sectors": "0x180",
+            "mcuboot.read-granularity": 1,
+            "qspif.QSPI_MIN_PROG_SIZE": 1
+        },
         "K64F": {
             // Configure bootloader to live in the first sector of flash
             "target.memory_bank_config": {