C6X gas: Remove "-matomic" option

[Joseph S. Myers]

On Thu, 3 Feb 2011, Bernd Schmidt wrote:

> TI has decided that for convenience they'd prefer if -march=c64x+ simply
> enabled atomic instructions, even if they are not usable on all devices.
> The following patch implements this. Ok?

It seems to me that if you treat these instructions as present on all 
C64x+ and C674x then you should no longer need TIC6X_INSN_ATOMIC at all; 
the instructions in question should just be marked as TIC6X_INSN_C64XP 
instead.

-- 
Joseph S. Myers
joseph@codesourcery.com