ec/google/chromeec: hide absent battery and MKBP devices

[jackadam1981]

Summary

Use Chrome EC feature bits to hide Chrome OS laptop-oriented ACPI devices when the EC reports that the hardware is not present.

• Return _STA = 0 for the ACPI battery device when neither BATT nor SBAT is reported by the EC.
• Return _STA = 0 for the Chrome EC MKBP keyboard/buttons device (GOOG0007) when the EC does not report KEYB.
• Leave the main Chrome EC command device (GOOG0004) and AC adapter (ACPI0003) visible, because charger/PD/EC command functionality can still be valid on Chromebox-style systems.

Rationale

Kaisa-style Chromebox systems can share Chrome EC ACPI code with Chromebook designs, but the EC feature bitmap already tells us whether battery and EC keyboard/button capabilities exist. Hiding these devices via _STA avoids exposing non-functional laptop devices to the OS without adding board-specific policy knobs.

Validation

Built google/puff Kaisa from MrChromebox-2603 with a release iPXE payload.

• Build tree: /home/jack/coreboot_build/src/coreboot-2603-chromeec-acpi-pr
• Build log: /home/jack/coreboot_build/out/logs/build-kaisa-2603-release-ipxe-only-chromeec-acpi-sta-20260601-170324.log
• Archived ROM: /home/jack/coreboot_build/out/roms/kaisa-2603-release-ipxe-only-chromeec-acpi-sta-20260601-171620/kaisa-2603-release-ipxe-only-chromeec-acpi-sta.rom
• SHA256: 458babe81b708f3a5acbd1a3971afcfcca5e4daff1bc9c74f9887fdd70ac03bf

Flashed the ROM on a Kaisa target using the local MrChromebox-style flash script, preserving/injecting platform data from the backup.

• Flash backup: /home/jack/文档/CoreBoot-Build/out/backups/backup_20260602_011854.rom
• Flash verification: VERIFIED

After reboot on the target:

• PNP0C0A:00 battery path \_SB_.PCI0.LPCB.EC0_.BAT0 reports status=0.
• GOOG0007:00 path \_SB_.PCI0.LPCB.EC0_.CREC.CKSC reports status=0.
• cros_ec_buttons is no longer present in /sys/class/input.
• GOOG0004:00 remains present with status=15.
• ACPI0003:00 remains present with status=15.
• The regular Power Button input remains present.
• /sys/class/power_supply still exposes AC, CROS_DEDICATED_CHARGER, and CROS_USBPD_CHARGER0.

Note: the flashed validation ROM contained only this PR's change on top of MrChromebox-2603, so unrelated Kaisa eMMC hiding work was not included in this runtime test image.

[MrChromebox]

looks good at first glance, just need to verify no issues on devices that don't support the EC feature flag

[MrChromebox]

here's the version I upstreamed, seems to work properly in my limited testing: https://review.coreboot.org/c/coreboot/+/93260

just added a check for the DFUD flag before using the feature flags to determine status