Reduce number of parallel builds

Reduce number of parallel builds

With recent introduction of C++ code required memory for each compiler
instance has significantly increased causing build issues.

Currently build system spins 2 compiler instances per logical CPU core.

As CPU can hardly execute more than one thread at a time, it should be
pretty safe to change that formula so it doesn't multiply number of cpu
cores by 2 and such change will signifucantly reduce amount of memory
needed.

Change-Id: Ic829fff6e45f4caf98a6d9c1c98c53ed003039ef
Signed-off-by: Damjan Marion <damarion@cisco.com>