[Porting] Update the readme file.
Add new board in the README.md file.
* ARM
* Cortex-M0
* [eml3047](./eml3047/README.md)
+ * [frdmkl26z](./frdmkl26z/README.md)
* [frdmkl27z](./frdmkl27z/README.md)
+ * [frdmkl28z](./frdmkl28z/README.md)
+ * [frdmkl43z](./frdmkl43z/README.md)
+ * [frdmkl81z](./frdmkl81z/README.md)
+ * [frdmkl82z](./frdmkl82z/README.md)
* Cortex-M3
* [mk1101](./mk1101/README.md)
* Cortex-M4
