ci: build tftf with -j=ncores

Tftf can build with lots of cores just fine but they are never given to
the make command. Allow this on local runs.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: I982b2bc9d2e6519042c665e01b9b3d709b25a03f
1 file changed