ARM: highbank: use wfi macro instead of inline asm

Older compilers don't recognize v7 wfi instruction, so use wfi macro to
fix builds on old compilers.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
diff --git a/board/highbank/highbank.c b/board/highbank/highbank.c
index f41bf05..09cd45d 100644
--- a/board/highbank/highbank.c
+++ b/board/highbank/highbank.c
@@ -88,5 +88,6 @@
 void reset_cpu(ulong addr)
 {
 	writel(HB_PWR_HARD_RESET, HB_SREG_A9_PWR_REQ);
-	asm("	wfi");
+
+	wfi();
 }