t480s: add p-state patch from https://review.coreboot.org/c/coreboot/+/91173

[tlaurion]

Fix #2120

repro

cd ~
git clone https://github.com/linuxboot/heads
cd heads
./docker_repro.sh make BOARD=EOL_t480s-maximized
cd build/x86/coreboot-25.09/
git fetch https://review.coreboot.org/coreboot refs/changes/73/91173/2 && git format-patch -1 --stdout FETCH_HEAD > ../../../patches/coreboot-25.09/0013-sklkbl_thinkpad-Enable_ACPI_P-state_table_generation.patch
cd ~/heads
./docker_repro.sh make BOARD=EOL_t480s-maximized real.remove_canary_files-extract_patch_rebuild_what_changed
./docker_repro.sh make BOARD=EOL_t480s-maximized
[...]
INFO: Applying patch file: patches/coreboot-25.09/0013-sklkbl_thinkpad-Enable_ACPI_P-state_table_generation.patch
Checking patch build/x86/coreboot-25.09/src/mainboard/lenovo/sklkbl_thinkpad/devicetree.cb...
Applied patch build/x86/coreboot-25.09/src/mainboard/lenovo/sklkbl_thinkpad/devicetree.cb cleanly.
[...]

Please test artifacts @James333666999

[Copilot]

Pull request overview

Adds an upstream coreboot patch to the coreboot-25.09 patchset to enable ACPI P-state table generation on Lenovo sklkbl_thinkpad (fixing missing ACPI _PSS/_PCT/_PPC tables reported for T480s / issue #2120).

Changes:

• Add coreboot patch 91173 to set eist_enable=true in src/mainboard/lenovo/sklkbl_thinkpad/devicetree.cb, enabling ACPI P-state table generation.

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