boardid: Switch from Kconfig to weak functions

This patch switches the board_id and ram_code helper framework to use
weak functions rather than Kconfigs to determine whether the board
supplies these IDs. This cuts down on the amount of boilerplate Kconfigs
many boards have to set and also gives them more flexibility, such as
being able to determine at runtime whether a given ID is present.

Change-Id: I97d6d1103ebb2a2a7cf1ecfc45709c7e8c1a5cb0
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/22695
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/intel/kunimitsu/Kconfig

@@ -2,7 +2,6 @@ if BOARD_INTEL_KUNIMITSU
 
 config BOARD_SPECIFIC_OPTIONS # dummy
 	def_bool y
-	select BOARD_ID_AUTO
 	select BOARD_ROMSIZE_KB_16384
 	select DRIVERS_GENERIC_MAX98357A
 	select DRIVERS_I2C_GENERIC