x86/resctrl: Merge the ctrlval arrays

Now that the CODE/DATA resources don't use overlapping slots in the
ctrlval arrays, they can be merged. This allows the cdp_peer configuration
to be read from any resource's domain, instead of searching for the matching
flavour.

Add a helper to allocate the ctrlval array, that returns the value on the
L2 or L3 resource if it already exists. This gets removed once the
resources are merged, and there really is only one ctrlval array.

Signed-off-by: James Morse <james.morse@arm.com>