toolchain-external: add ADI Blackfin 2014R1 toolchain, remove 2012R1

This commit adds support for two ADI Blackfin toolchains: the 'stable'
2014R1 based on gcc 4.3, and the 'experimental' 2014R1 based on gcc
4.5.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>