toolchain-external: CodeSourcery PowerPC: Revert the removal of CS PowerPC 2011.03

toolchain-external: CodeSourcery PowerPC: Revert the removal of CS PowerPC 2011.03

As reported by Yann E. MORIN [1], the latest CS PowerPC toolchain (2012.03)
requires a PPC CPU with SPE, which is basically two variants, 8540 (e500v1) and
8548 (e500v2) in Buildroot. All other PPC CPU can't use that toolchain.

Keep CS PowerPC 2011.03 as latest available version and add a second Kconfig
symbol for the CS PowerPC 2012.03 since it's verry specific to one CPU type
(e500v2).

Previously it was possible to select the CS 2012.03 with a powerpc 8540 (e500v1)
CPU but the sysroot provided by the toolchain only support the 8548 (e500v2)
variant. Allow to select CS 2012.03 only with BR2_powerpc_8548.

Also re-add the previous CS toolchain handling for pixman and liquid-dsp.

[1] http://lists.busybox.net/pipermail/buildroot/2015-December/148308.html

Reported-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>