Device tree changes to boot FreeBSD on FVPs

FreeBSD does not understand #interrupt-map in a device tree. This prevents the
GIC from being set up correctly. This patch removes the #interrupt-map in the
device trees for the Base and Foundation FVPs. This enables correct boot of
FreeBSD on these platforms.

These changes have been tested with FreeBSD and an Ubuntu cloud image
(ubuntu-16.04-server-cloudimg-arm64-uefi1.img) to ensure compatibility with
Linux.

Change-Id: I1347acdcf994ec4b1dd843ba32af9951aa54db73
Signed-off-by: Achin Gupta <achin.gupta@arm.com>