Use coreboot build system for libpayload, too.

Use coreboot build system for libpayload, too.

This change makes building coreboot related projects more unified.

Change-Id: I0f1181e2fffde1e03675523f7dc9eef3119052c3
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/71
Tested-by: build bot (Jenkins)
Reviewed-by: Uwe Hermann <uwe@hermann-uwe.de>