plat/arm: Introduce A5 DesignStart platform.

This patch adds support for Cortex-A5 FVP for the
DesignStart program. DesignStart aims at providing
low cost and fast access to Arm IP.

Currently with this patch only the primary CPU is booted
and the rest of them wait for an interrupt.

Signed-off-by: Usama Arif <usama.arif@arm.com>
Change-Id: I3a2281ce6de2402dda4610a89939ed53aa045fab