Fix ROM size for STM32WB55RGVx (16 MB -> 1 MB)

Per feedback from STM the correct ROM size is 1 MB, instead of
16 MB. The KEIL source information is (in the pack itself) wrong, since
the KEIL webpage lists it as a 16 MB part, too - but if you look into
other sources - it is indeed 1 MB.

Author: Janne Kiiskila

tools/arm_pack_manager/index.json

@@ -462678,7 +462678,7 @@
               "non_secure_callable": false
             },
             "start": 134217728,
-            "size": 16777216,
+            "size": 1048576,
             "startup": true,
             "default": true
           },
@@ -462702,7 +462702,7 @@
           {
             "file_name": "CMSIS/Flash/STM32WB_M4.FLM",
             "start": 134217728,
-            "size": 16777216,
+            "size": 1048576,
             "default": true,
             "ram_start": null,
             "ram_size": null