power: remove support for ondemand_boost_cpu

This is not not supported in the version of the ondemand governor
that we are using.

Change-Id: Ie83bb841f1b77aa6b26af20546ae29f7a5dc37b0
dlx: defconfig: set ondemand as the default governor

Change-Id: Iea98f267c3da20496d46a327708302d368da44d8