Add bsp-specific build configuration from build/

- Bring in some board-specific files from build/: sdcard, recovery,
bootloader (formerly u-boot.mk). Also, add includable stubs for pbuilder
rules that belong in the bsp repository, and for package lists to
install in the rootfs.

Change-Id: Ie59915219429a7c58023185460f838e0edc93247
5 files changed