soc/intel/skylake: Disable s0ix if not enabled in devicetree
There is an enable_s0ix config option in the devicetree that should
be used to disable it when not set:
- do not export C8/C9/C10 C-states in _CST
- do not enable SLP_S0 in FSP
BUG=chrome-os-partner:58666
TEST=test on eve board to ensure that OS only sees 3 ACPI C-states
instead of 6 and that it no longer attempts to enter C10
Change-Id: I90e4dc776d1d17d0b700cda63c8476786cd2e4ff
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/18394
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>