Project and mbed target updates.

- Updated register headers to merged versions.
- Added standard linker config files for supported chips in src/linker.
- Removed old KL25 mbed HAL, now using common KLXX HAL.
- Moved mbed cmsis.h and cmsis_nvic.* for each target to HAL dirs.
- Added KSDK based mbed target HAL support for K64F12 and K22F51212.
- Updated IAR demo projects for KL25 and K64 to build with these changes.
- Enabled mbed for K64 in demo project.