{ec,mb}/system76: Replace color keyboard logic

System76 EC since system76/ec@9ac513128a detects if the keyboard is
white or RGB backlit via `RGBKB-DET#` at runtime. Remove the Kconfig for
the selection and update the ACPI methods for the new functionality.

Change-Id: I60d3d165a58e30d2afc8736c0eb64dd90c8227ca
Signed-off-by: Tim Crawford <tcrawford@system76.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76152
Reviewed-by: Jeremy Soller <jeremy@system76.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/system76/addw1/Kconfig

@@ -8,7 +8,6 @@ config BOARD_SPECIFIC_OPTIONS
 	select DRIVERS_I2C_HID
 	select DRIVERS_I2C_TAS5825M
 	select EC_SYSTEM76_EC
-	select EC_SYSTEM76_EC_COLOR_KEYBOARD
 	select EC_SYSTEM76_EC_DGPU
 	select EC_SYSTEM76_EC_OLED
 	select HAVE_ACPI_RESUME