aemfvp-a: Add fix for DTB name.

The upstream u-boot configuration requires a specific name for the
DTB. This changes creates a copy of the built FVP with the correct
name.

aemfvp-a-rme: Add fix for download path

aemfvp-a-rme: Update toolchain

Upgrade the cross compile toolchain to 13.2.rel1 and change the
buildroot config so that it uses the installed toolchain instead
of building it's own version.

Signed-off-by: Ben Taylor <ben.taylor@linaro.org>
Change-Id: I3f98f139c3852d414f2c3b4ecad7dba5a6493475