spl: Convert boot_device into a struct

At present some spl_xxx_load_image() functions take a parameter and some
don't. Of those that do, most take an integer but one takes a string.

Convert this parameter into a struct so that we can pass all functions the
same thing. This will allow us to use a common function signature.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/common/spl/spl_net.c b/common/spl/spl_net.c
index f417d17..730f88e 100644
--- a/common/spl/spl_net.c
+++ b/common/spl/spl_net.c
@@ -14,7 +14,7 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
-int spl_net_load_image(const char *device)
+int spl_net_load_image(struct spl_boot_device *bootdev)
 {
 	int rv;
 
@@ -27,8 +27,8 @@
 		printf("No Ethernet devices found\n");
 		return -ENODEV;
 	}
-	if (device)
-		setenv("ethact", device);
+	if (bootdev->boot_device_name)
+		setenv("ethact", bootdev->boot_device_name);
 	rv = net_loop(BOOTP);
 	if (rv < 0) {
 		printf("Problem booting with BOOTP\n");