nios2: Switch to generic __xchg()
nios2: Switch to generic __xchg()

The generic __xchg() implementation present in asm-generic/cmpxchg.h is
correct on nios2 and even generates the same code. Switch to this generic
implementation to trim down the amount of ad-hoc copies of the code.

Signed-off-by: Marek Vasut <f40600653b33f5282fa4c5daf377dfc444fb4625@denx.de>
Acked-by: Ley Foon Tan <95f178e5e278816be0436ff61f034a97684bdd0e@altera.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs