Added -p <N> parallel building option

[giuliobenetti]

Building can be faster.

Added -p option, where N is passed to sub-Makefile as -jN

Signed-off-by: Giulio Benetti giulio.benetti@micronovasrl.com

[sergey-suloev]

@giuliobenetti it is very fast for me already, like 10 sec )

[giuliobenetti]

@sergey-suloev yes it is fast, but with parallel building can be faster 3-4x. Can you give it a try?

[sergey-suloev]

@giuliobenetti ok