Fix Skylake PEBS data source for perf

[Andi Kleen]

Fix data source reporting for Skylake and Skylake Server.
The encodings have changed to express support for L4 and persistent
memory. 

The first patch is a (independent) cleanup.

The second is for the kernel and the third for perf/tools.
The kernel part and perf tools will compile independently.

v1:
Initial post
v2:
Merged some patches.
Change encoding to use special bit for each combination instead
of modifiers.
v3: 
Switch to new generic lvlnum indication
v4:
Repost. No changes.