tools: PCI: Change pcitest compiling process

Change tool compiling process in order to be build using the same
mechanism used in other linux tools (e.g. iio, perf, etc). This will
allow in future the buildroot tool to build and integrate this tool in
a more expeditious way.

Update documentation accordingly.

Signed-off-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Kishon Vijay Abraham I <kishon@ti.com>