Folder re-org to fit new MCU K22F variances

This is a simple re-structure of the K22F folder to allow other MCU
variances to land here.
Created the MCU_K22F512 device but left the 'K22F' as a target for
the FRDM-K22F board.

Rebased to master

targets/TARGET_Freescale/mbed_rtx.h

@@ -47,7 +47,7 @@
 #define OS_CLOCK                96000000
 #endif
 
-#elif defined(TARGET_K22F)
+#elif defined(TARGET_MCU_K22F)
 
 #ifndef INITIAL_SP
 #define INITIAL_SP              (0x20010000UL)

targets/targets.json

@@ -482,11 +482,11 @@
         "release_versions": ["2"],
         "device_name": "MK20DX256xxx7"
     },
-    "K22F": {
+    "MCU_K22F512": {
         "supported_form_factors": ["ARDUINO"],
         "core": "Cortex-M4F",
         "supported_toolchains": ["ARM", "GCC_ARM", "IAR"],
-        "extra_labels": ["Freescale", "KSDK2_MCUS", "FRDM", "KPSDK_MCUS", "KPSDK_CODE"],
+        "extra_labels": ["Freescale", "KSDK2_MCUS", "MCU_K22F", "MCU_K22F512", "FRDM", "KPSDK_MCUS", "KPSDK_CODE"],
         "is_disk_virtual": true,
         "macros": ["CPU_MK22FN512VLH12", "FSL_RTOS_MBED"],
         "inherits": ["Target"],
@@ -495,6 +495,10 @@
         "release_versions": ["2", "5"],
         "device_name": "MK22DN512xxx5"
     },
+    "K22F": {
+        "inherits": ["MCU_K22F512"],
+        "extra_labels_add": ["FRDM"]
+    },
     "KL27Z": {
         "inherits": ["Target"],
         "core": "Cortex-M0+",