Revert "toolchain: allow side by side sysroot directories"

Revert "toolchain: allow side by side sysroot directories"

This reverts commit 9a1e9efe2618ebbf12ed2567bcd6e8cca5619547.

Currently Codescape toolchains cannot be used to generate a big endian
root file system because the support for side by side sysroots is not
complete.

There is a patch [1] waiting in the queue which fixes the issue for the
current version of Codescape toolchains we have, but it will not work
for the next one that is coming. So, instead of messing more with the
toolchain infra I think it's better to handle these specific Codescape
toolchain's weirdness in hooks which won't affect others.

[1]: http://patchwork.ozlabs.org/patch/571708/

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>