x86: Don't process the kernel command line unless enabled

If the 'bootm' command is not enabled then this code is not available and
this causes a link error. Fix it.

Note that for the EFI app, there is no indication of missing code. It just
hangs!

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/arch/x86/lib/zimage.c b/arch/x86/lib/zimage.c
index 7ce0222..9cc0449 100644
--- a/arch/x86/lib/zimage.c
+++ b/arch/x86/lib/zimage.c
@@ -365,11 +365,14 @@
 			strcpy(cmd_line, (char *)cmdline_force);
 		else
 			build_command_line(cmd_line, auto_boot);
-		ret = bootm_process_cmdline(cmd_line, max_size, BOOTM_CL_ALL);
-		if (ret) {
-			printf("Cmdline setup failed (max_size=%x, bootproto=%x, err=%d)\n",
-			       max_size, bootproto, ret);
-			return ret;
+		if (IS_ENABLED(CONFIG_CMD_BOOTM)) {
+			ret = bootm_process_cmdline(cmd_line, max_size,
+						    BOOTM_CL_ALL);
+			if (ret) {
+				printf("Cmdline setup failed (max_size=%x, bootproto=%x, err=%d)\n",
+				       max_size, bootproto, ret);
+				return ret;
+			}
 		}
 		printf("Kernel command line: \"");
 		puts(cmd_line);