Add support for using the Kconfig

With Kconfig support for external modules, We can now enable/disable the
configs using the defconfig. This change removes the hardcoded
KBUILD_OPTIONS and adds kleaf support for visibility to the Kconfig
file.

Signed-off-by: Will McVicker <willmcvicker@google.com>
Change-Id: I0a111c0621799f15db82f4449c2051df016a7275