conf: Refactor storing and usage of feature flags

conf: Refactor storing and usage of feature flags

Currently we were storing domain feature flags in a bit field as the
they were either enabled or disabled. New features such as paravirtual
spinlocks however can be tri-state as the default option may depend on
hypervisor version.

To allow storing tri-state feature state in the same place instead of
having to declare dedicated variables for each feature this patch
refactors the bit field to an array.