From: Tomáš Ďurovec <tomas.durovec@pantheon.tech>

Given a pre-built DPDK repository can be supplied to DTS, there is no
need to define multiple build targets. To simplify the process this
change makes each test run use only one DPDK build whether it's
pre-built or it needs to be built by DTS.

Signed-off-by: Tomáš Ďurovec <tomas.durovec@pantheon.tech>
Signed-off-by: Luca Vizzarro <luca.vizzarro@arm.com>