Samsung SoC drivers changes for v5.11

1. Limit the big.LITTLE cpuidle driver to Peach-Pit/Pi Chromebooks only
   because these are the only platforms were the driver works properly.
2. Convert the Exynos CLKOUT driver to a full module which solves
   boot-probe ordering issues (e.g. if device nodes in DTS are moved).
   This also brings modularization and compile testing.
3. Few minor cleanups in documentation and code.