build-scripts: add -a parameter for removing pci & smmu nodes

This patch adds new build flag -a to build scripts which is used
only when building for FVP_Base_AEMv8A-ARMv8A model. Since this
model doesn't has PCI & SMMU IPs (whereas the device tree has),
user lands in kernel panic while booting Linux in this model.

By passing -a true while building, the PCI & SMMU nodes are
removed in device-tree by which kernel panic is avoided.

Change-Id: I1f47ec1b216bf63bfbca50c05748fe5f8d8d22c2
Signed-off-by: Manoj Kumar <manoj.kumar3@arm.com>