Sconfig: parse Kconfig options from devicetree.cb

Sconfig: parse Kconfig options from devicetree.cb

Mainboard and chip Kconfig files have several build options that
are redundant with information in devicetree.cb. This patch enables
sconfig to auto-generate equivalent configuration.

  sconfig -s

Generates mainboard's static.c file, as before.

  sconfig -b

This operation creates mainboard's bootblock init code. By default,
for every chip listed in mainboard/devicetree.cb, if there is a
chip/bootblock.c file, the init function is called.
A mainboard/bootblock.c file can be added to override default
behaviour.

  sconfig -k

This operation generates select -options for component paths.

Change-Id: I808d44af552dbc5e0565d6a0f4f72c7be9f5740e
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/472
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>