libpayload: Add coreboot commonlib/bsd include path

Make BSD part of the coreboot commonlib accessible to libpayload.

Change-Id: I09f475d399ab785f3d3ffdb4b42950d2b397845e
Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59697
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <patrick@coreboot.org>

payloads/libpayload/Makefile

@@ -34,6 +34,7 @@ CC_real:=$(CC)
 endif
 
 export top := $(CURDIR)
+export coreboottop ?= $(abspath $(top)/../../)
 export src := src
 export srck := $(abspath $(top)/../../util/kconfig)
 export obj ?= build