process.c: Reduce maximum number of parallel jobs on UP machines

process.c: Reduce maximum number of parallel jobs on UP machines

We generally don't see sinlge-cpu systems any more in other than
embedded devices, where chances of being very low in RAM is a very
real possibility. If the maximum number of parallel jobs is too large
there, is is quite possible that we run out of memory on such systems.

Reducing the number of jobs makes such devies much less likely to
exceed their memory capacity.

Signed-off-by: Timo Kokkonen <timo.t.kokkonen@iki.fi>