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 <Baohua.Song@csr.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/cache-l2x0.c

@@ -37,7 +37,7 @@ static inline void cache_wait_way(void __iomem *reg, unsigned long mask)
 {
 	/* wait for cache operation by line or way to complete */
 	while (readl_relaxed(reg) & mask)
-		;
+		cpu_relax();
 }
 
 #ifdef CONFIG_CACHE_PL310