image: Drop IMAGE_BOOT_GET_CMDLINE

This is not needed with Kconfig, since we can use IS_ENABLED() easily
enough and the board code is now in a separate file. Update the only place
where this is used and drop it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
diff --git a/common/image-board.c b/common/image-board.c
index cb2479f..6565f01 100644
--- a/common/image-board.c
+++ b/common/image-board.c
@@ -898,7 +898,7 @@
 	if (CONFIG_IS_ENABLED(OF_LIBFDT))
 		boot_fdt_add_mem_rsv_regions(lmb, *of_flat_tree);
 
-	if (IMAGE_BOOT_GET_CMDLINE) {
+	if (IS_ENABLED(CONFIG_SYS_BOOT_GET_CMDLINE)) {
 		ret = boot_get_cmdline(lmb, &images->cmdline_start,
 				       &images->cmdline_end);
 		if (ret) {