LOCAL: build_all.py: allow alternate build targets.

Allow make targets to be given to build-all.py, which
in turn allows the build-all preverification step to be used to
generate all kernel artifacts for later preverification steps.
This moves us closer to eliminating the need to build the kernel
twice for each commit to be tested by the PV framework.

Change-Id: Ifacdbb161604f06f85f4248f21998dda282e6fd0
Signed-off-by: Gregory Bean <gbean@codeaurora.org>
(cherry picked from commit 81a73760834ee3c0b3b1ab3010fd6530d5b82313)