[Intel-gfx] i915/display: split and constify vtable (v4)

[Dave Airlie]

v4: I know I could have resent one patch but there was a bit of
rebase fallout from it, and it had another subtle bug, I also
fixed the kerneldoc.

(v3 just adds some missing ,)

      Details below, I've taken all the review feedback (thanks Jani).
I added 3 patches moving to wrappers before refactoring, and
one other patch is unreviewed (07) but the main comment was wanting
the wrappers.

Jani if you are happy with the final 4 patches can you land this
series, I don't think I have drm-intel commit rights.

v1:
This is orthogonal to my display ptr refactoring and should probably
be applied first.

The display funcs vtable was a bit of mess, lots of intermixing of
internal display functionality and interfaces to watermarks/irqs.

It's also considered not great security practice to leave writeable
function pointers around for exploits to get into.

This series attempts to address both problems, first there are a
few cleanups, then it splits the function table into multiple pieces.
Some of the splits might be bikesheds but I think we should apply first
and merge things later if there is good reason.

The second half converts all the vtables to static const structs,
I've used macros in some of them to make it less messy, the cdclk
one is probably the worst one.

v2:
Added some patches adding wrappers around things before refactoring
them as suggested by Jani.
Fixed up all struct names as suggested by Jani.
Added s-o-b lines
Added commit msgs.

v3:
added missing , (Jani)

v4:
fix wm bug the crept in (Jani), fix kernel doc warning (CI)

Dave.