arch/arm: OABI is no more, switch to only EABI

Well, leave the prompt as an OBSOLETE thing, scheduled to
be removed soon.

As an indication OABI lives its last days, gcc-4.8 will no
longer recognise non-EABI targets.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 reporter_name="Ioannis E. VENETIS"

 reporter_url="http://sourceware.org/ml/crossgcc/2009-11/msg00109.html"

 reporter_comment=""