libpayload/Makefile: Improve object files list creation

This patch ports some parts of main coreboot Makefile to the libpayload
Makefile in order to improve object files creation.

Moreover, the coreboot source files are now accessible an will be
correctly compiled under libpayload build directory.

Change-Id: If1280c0a3f7e99aad2ecf8a0379a98af31ccefc3
Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59843
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <patrick@coreboot.org>

0 files changed, 0 insertions, 0 deletions