barriers: Move __DSB() to the new API

Remove the arch-specific ARM-centric __DSB() macro and use the new
barrier API instead.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>

soc/arm/renesas_rcar/gen3/soc.c

@@ -8,6 +8,7 @@
 #include <zephyr/kernel.h>
 #include <zephyr/device.h>
 #include <zephyr/init.h>
+#include <zephyr/sys/barrier.h>
 
 /**
  *
@@ -33,7 +34,7 @@ void z_arm_platform_init(void)
 
 	/* Invalidate instruction cache and flush branch target cache */
 	__set_ICIALLU(0);
-	__DSB();
+	barrier_dsync_fence_full();
 	__ISB();
 
 	L1C_EnableCaches();