irqchip/gic-v3: Use nops macro for Cavium ThunderX erratum 23154

The workaround for Cavium ThunderX erratum 23154 has a homebrew
pipeflush built out of NOP sequences around the read of the IAR.

This patch converts the code to use the new nops macro, which makes it
a little easier to read.
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/include/asm/arch_gicv3.h

@@ -122,14 +122,9 @@ static inline u64 gic_read_iar_cavium_thunderx(void)
 {
 	u64 irqstat;
 
-	asm volatile(
-		"nop;nop;nop;nop\n\t"
-		"nop;nop;nop;nop");
-
+	nops(8);
 	irqstat = read_sysreg_s(ICC_IAR1_EL1);
-
-	asm volatile(
-		"nop;nop;nop;nop");
+	nops(4);
 	mb();
 
 	return irqstat;