rockchip: rk3188: rock: adjust for SPL/TPL split

With the changes to split SPL/TPL for the RK3368, I apparently missed
some needed adjustments to the RK3188 Kconfig and rock_defconfig.

This fixes build-issues for the rock board after applying the RK3368
enablement (and SPL/TPL) set that resulted from TPL_SERIAL_SUPPORT,
TPL_ROCKCHIP_BACK_TO_BROM and TPL_TINY_MEMSET being separate symbols
now.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/Kconfig b/lib/Kconfig
index 2f5a210..8163617 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -61,6 +61,15 @@
 	  size-constrained envrionments even this may be too big. Enable this
 	  option to reduce code size slightly at the cost of some speed.
 
+config TPL_TINY_MEMSET
+	bool "Use a very small memset() in TPL"
+	help
+	  The faster memset() is the arch-specific one (if available) enabled
+	  by CONFIG_USE_ARCH_MEMSET. If that is not enabled, we can still get
+	  better performance by writing a word at a time. But in very
+	  size-constrained envrionments even this may be too big. Enable this
+	  option to reduce code size slightly at the cost of some speed.
+
 config RBTREE
 	bool