utils/cbfstool: Import coreboot util cbfstool

We need this to construct a flashable image.

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Makefile: build cbfstools as a target

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
cpu/cpu.gpr: fix bootblock.elf naming

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
cpu/Makefile: build flashable image out of bootblock

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>