rockchip: back-to-bootrom: simplify the #ifdef-check for LIBCOMMON in TPL/SPL

With the finer-grained control over LIBCOMMON_SUPPORT for TPL/SPL (i.e.
with the newly introduced distinction between TPL_LIBCOMMON_SUPPORT and
SPL_LIBCOMMON_SUPPORT), we can simplify the #ifdef-check to simply use
CONFIG_IS_ENABELD.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
[fixed up to use 'puts' and LIBCOMMON:]
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

arch/arm/mach-rockchip/bootrom.c

@@ -9,8 +9,8 @@
 
 void back_to_bootrom(void)
 {
-#if defined(CONFIG_SPL_LIBCOMMON_SUPPORT) && !defined(CONFIG_TPL_BUILD)
-	puts("Returning to boot ROM...");
+#if CONFIG_IS_ENABLED(LIBCOMMON_SUPPORT)
+	puts("Returning to boot ROM...\n");
 #endif
 	_back_to_bootrom_s();
 }