linuxboot: add rdedmunds as supported platform

Enable linuxboot test for RD-Edmunds platform.

This is an initial implementation of linuxboot for RD-Edmunds platform
and not the final version.

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I344d1adbb5306b8c430e8f456d775046d3c9a392