global: Convert simple_strtoul() with decimal to dectoul()

It is a pain to have to specify the value 10 in each call. Add a new
dectoul() function and update the code to use it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/net/pfe_eth/pfe_firmware.c b/drivers/net/pfe_eth/pfe_firmware.c
index ac86e33..ad5bc3c 100644
--- a/drivers/net/pfe_eth/pfe_firmware.c
+++ b/drivers/net/pfe_eth/pfe_firmware.c
@@ -298,7 +298,7 @@
 	if (!p) {
 		max_fw_count = 2;
 	} else {
-		max_fw_count = simple_strtoul(p, NULL, 10);
+		max_fw_count = dectoul(p, NULL);
 		if (max_fw_count)
 			max_fw_count = 3;
 		else