build system: mark sub-make invocations as parallelizable

We rely on gnu make, so we can expect the jobserver to be around in
parallel builds, too. Avoids some make warnings and slightly speeds up
the build if those sub-makes are executed (eg for arm-trusted-firmware
and vboot).

Change-Id: I0e6a77f2813f7453d53e88e0214ad8c1b8689042
Signed-off-by: Patrick Georgi <>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <>
Reviewed-by: Martin Roth <>
4 files changed