console: Don't enable CONFIG-CONSOLE_MUX, etc. in SPL

CONFIG_CONSOLE_MUX and CONFIG_SYS_CONSOLE_IS_IN_ENV are not applicable
for SPL. Update the console code to use CONFIG_IS_ENABLED(), so that these
options will be inactive in SPL.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/common/usb_kbd.c b/common/usb_kbd.c
index 5f9a64a..d2d29cc 100644
--- a/common/usb_kbd.c
+++ b/common/usb_kbd.c
@@ -516,7 +516,7 @@
 		return error;
 
 	stdinname = getenv("stdin");
-#ifdef CONFIG_CONSOLE_MUX
+#if CONFIG_IS_ENABLED(CONSOLE_MUX)
 	error = iomux_doenv(stdin, stdinname);
 	if (error)
 		return error;
@@ -581,7 +581,7 @@
 		data = usb_kbd_dev->privptr;
 		if (stdio_deregister_dev(dev, force) != 0)
 			return 1;
-#ifdef CONFIG_CONSOLE_MUX
+#if CONFIG_IS_ENABLED(CONSOLE_MUX)
 		if (iomux_doenv(stdin, getenv("stdin")) != 0)
 			return 1;
 #endif
@@ -626,7 +626,7 @@
 		ret = -EPERM;
 		goto err;
 	}
-#ifdef CONFIG_CONSOLE_MUX
+#if CONFIG_IS_ENABLED(CONSOLE_MUX)
 	if (iomux_doenv(stdin, getenv("stdin"))) {
 		ret = -ENOLINK;
 		goto err;