Rework the vboot_reference make system.

After this change the generated files are placed in a
separate tree (such thet they don't show in the
`git status' output anymore) and the dependencies are
followed properly (if a .h file changes the
appropriate .o files and apps get rebuilt).

Tested as follows:

> $ make clean
> $ make # build succeeds
> $ git status # shows clean directory
> $ RUNTESTS=1 make # (captured test output matches that of the test run before any changes)
> $ touch ./vboot_firmware/include/tlcl.h
> $ make  # make succeeds
> $ find build -type f -newer ./vboot_firmware/include/tlcl.h
build/vboot_firmware/lib/rollback_index.o
build/vboot_firmware/lib/rollback_index.o.d
build/vboot_firmware/a.out
build/vboot_fw.a
build/utility/vbutil_key
build/utility/kernel_utility.d
build/utility/vbutil_key.d
build/utility/verify_data
build/utility/load_kernel_test.d
build/utility/vbutil_keyblock.d
build/utility/vbutil_kernel
build/utility/vbutil_kernel.d
build/utility/firmware_utility
build/utility/signature_digest_utility.d
build/utility/kernel_utility
build/utility/verify_data.d
build/utility/vbutil_keyblock
build/utility/signature_digest_utility
build/utility/load_kernel_test
build/utility/firmware_utility.d
build/tests/vboot_common3_tests
build/tests/vboot_common2_tests
build/host/a.out
$ >

Review URL: http://codereview.chromium.org/2845001
16 files changed