[POWERPC] Miscellaneous arch/powerpc Kconfig and platform/Kconfig cleanup

* Cleaned up some whitespace in arch/powerpc/Kconfig
* Moved sourcing of platforms/embedded6xx/Kconfig into platform/Kconfig
* Moved sourcing of platforms/4xx/Kconfig into platform/Kconfig and disabled it
* Removed EMBEDDEDBOOT since its not supported in arch/powerpc
* Removed PC_KEYBOARD since its not used anywhere
* Moved a few CONFIG options around in platform/Kconfig
* Moved interrupt controllers into platform/Kconfig out of bus section

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>