ARM: 7089/1: L2X0: add explicit cpu_relax() for busy wait loop

using cpu_relax in busy loops is a well-known idiom in the kernel.
It's more for documentation purposes than technically needed here.

Signed-off-by: Barry Song <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Reviewed-by: Jamie Iles <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/mm/cache-l2x0.c

···
 {
 	/* wait for cache operation by line or way to complete */
 	while (readl_relaxed(reg) & mask)
-		;
+		cpu_relax();
 }
 
 #ifdef CONFIG_CACHE_PL310