firmware: coreboot: Add CFR firmware attributes driver

coreboot can publish a CFR tree in its coreboot table to describe
firmware setup options. Add a firmware-attributes driver for that table
entry under the coreboot firmware driver directory.

The driver exposes runtime EFI variable-backed boolean, enum and integer
settings through the firmware-attributes ABI. It only registers settings
with readable runtime EFI variables, skips suppressed, volatile,
dependency-gated and non-runtime options, and keeps read-only or inactive
options read-only in sysfs.

For settings with an APM_CNT runtime-apply record, write the EFI
variable and ask firmware to apply the setting immediately with an I/O
port SMI command. If firmware reports a failure, restore the old EFI
variable value. Settings without a runtime apply hook keep the EFI
variable update and set pending_reboot. Depend on HAS_IOPORT because
APM_CNT uses legacy I/O ports.

Tested on a Star Labs Byte with firmware 26.07: runtime APM_CNT apply
was verified with power_led, and reboot-needed behavior was verified with
debug_level.

Link: https://doc.coreboot.org/drivers/cfr.html
Link: https://doc.coreboot.org/drivers/cfr_internal.html
Signed-off-by: Sean Rhodes <sean@starlabs.systems>
Link: https://lore.kernel.org/r/73204be94586622903da7fa90757fb091e8a7c2c.1788284852.git.sean@starlabs.systems
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>

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