Fix up PREEMPT configs

While preempt_dynamic was greatly improved at the beginning of the merge window, the config to make things work was messy and the new BEHAVIOUR configs were confusing to some. With commit a8b76910 the BEHAVIOUR config options are gone and we now default to whichever CONFIG_PREEMPT is selected. This MR moves us to the new config options, but should leave the kernel behaving as before with PREEMPT_VOLUNTARY as the default with PREEMPT_DYNAMIC enabled for all arches but s390 which does not enable DYNAMIC and builds with PREEMPT_NONE.

Signed-off-by: Justin M. Forbes jforbes@fedoraproject.org