of: use pr_fmt prefix for all console printing

Clean-up all the DT printk functions to use common pr_fmt prefix.

Some print statements such as kmalloc errors were redundant, so just
drop those.

Cc: Frank Rowand <frowand.list@gmail.com>
Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>
diff --git a/drivers/of/irq.c b/drivers/of/irq.c
index 1b58cd5..89a71c6 100644
--- a/drivers/of/irq.c
+++ b/drivers/of/irq.c
@@ -18,6 +18,8 @@
  * driver.
  */
 
+#define pr_fmt(fmt)	"OF: " fmt
+
 #include <linux/device.h>
 #include <linux/errno.h>
 #include <linux/list.h>