arm64: optimize smp_kick_all_cpus

gic_kick_secondary_cpus can directly return to the caller of
smp_kick_all_cpus.  We do not have to use x29 register here.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: York Sun <york.sun@nxp.com>

arch/arm/cpu/armv8/start.S

@@ -258,12 +258,10 @@ ENDPROC(lowlevel_init)
 
 WEAK(smp_kick_all_cpus)
 	/* Kick secondary cpus up by SGI 0 interrupt */
-	mov	x29, lr			/* Save LR */
 #if defined(CONFIG_GICV2) || defined(CONFIG_GICV3)
 	ldr	x0, =GICD_BASE
-	bl	gic_kick_secondary_cpus
+	b	gic_kick_secondary_cpus
 #endif
-	mov	lr, x29			/* Restore LR */
 	ret
 ENDPROC(smp_kick_all_cpus)