util,arch-arm: Added python script to generate ARM FS binaries

util,arch-arm: Added python script to generate ARM FS binaries

This python script builds the bootloaders, kernels and DTBs for the
VExpress_GEM5_V1 (aarch32/aarch64), VExpress_EMM and VExpress_EMM64
platforms (it checkouts some linux kernel repositories when needed).

This is the result of this e-mail thread in gem5-dev mailing list:
http://www.mail-archive.com/gem5-dev@gem5.org/msg22406.html

Change-Id: Ida8f9b974f7188f48be8f84f14828a1973d6d256
Signed-off-by: Pau Cabre <pau.cabre@metempsy.com>
Reviewed-on: https://gem5-review.googlesource.com/3945
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>