Revert "Update mbed framework to 5.11.0"

This reverts commit d4d207a.

Author: ivankravets

platform.json

@@ -31,7 +31,7 @@
     "framework-mbed": {
       "type": "framework",
       "optional": true,
-      "version": "~5.51100.181227"
+      "version": "~5.51001.1"
     },
     "tool-openocd": {
       "type": "debugger",