soc/intel/broadwell: Rework IGD's CDClk selection

CDClk selection was wrong in some corner cases (e.g. ULX SKUs) and,
for Broadwell, never took the devicetree config into account.

Rewrite the selection with the following in mind:

  o cpu_is_ult() might return `true` for ULX SKUs, too,

  o ULX and Broadwell-ULT SKUs can be `overclocked` with additional
    cooling, so leave that as devicetree option.

For Haswell, the following frequency selections are valid:

  o ULX: 337.5MHz by default, 450MHz optional
  o ULT: 450MHz only (maybe 337.5MHz too, documentation varies,
                      it wasn't selectable before either)
  o others: 540MHz by default, 450MHz optional

For Broadwell:

  o ULX: 450MHz by default, 337.5MHz / 540MHz optional
  o ULT: 540MHz by default, 337.5MHz / 450MHz / 675MHz optional
  o others: 667MHz by default, 337.5MHz / 450MHz / 540MHz optional

Side effects: A too high setting in the devicetree results in the
highest possible frequency now, Haswell non-ULT/ULX defaults to 540MHz
instead of 450MHz.

Change-Id: Iec12752f2a47bf4a5ae6077c75790eae9378c1b2
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/17768
Tested-by: build bot (Jenkins)
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>

0 files changed, 0 insertions, 0 deletions