soc/intel/braswell: Unify DPTF enablement

Currently, there are 3 separate settings for DPTF which are not always
in sync:
- the enabled/disabled state of the devicetree PCI device
- the 'dptf_enable' register, which sets the ACPI device status via GNVS
- the 'DptfDisable' register, which sets the FSP UPD of the same name

To make things sane, drop the two chip registers, and set the GNVS
variable and FSP UPD based on the enabled/disabled status of the DPTF
PCI device in the mainboard's devicetree.

TEST=build/boot google/cyan (edgar). Verify that the PCI and ACPI
devices are present/enabled when DPTF is enabled in devicetree, and not
present/disabled when disabled in devicetree.

Change-Id: I8fc1b63eda0dc2e047d9cb1e11a02d41ab8b2ad7
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78743
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>
diff --git a/src/soc/intel/braswell/chip.c b/src/soc/intel/braswell/chip.c
index ce394d0..d3c41f8 100644
--- a/src/soc/intel/braswell/chip.c
+++ b/src/soc/intel/braswell/chip.c
@@ -79,7 +79,7 @@
 	params->AzaliaConfigPtr			= 0;
 	params->PunitPwrConfigDisable		= config->PunitPwrConfigDisable;
 	params->ChvSvidConfig			= config->ChvSvidConfig;
-	params->DptfDisable			= config->DptfDisable;
+	params->DptfDisable			= !is_devfn_enabled(PCI_DEVFN(PUNIT_DEV, 0));
 	params->PcdEmmcMode			= config->PcdEmmcMode;
 	params->PcdUsb3ClkSsc			= 1;
 	params->PcdDispClkSsc			= 1;