Convert CONFIG_SYS_WHITE_ON_BLACK to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_WHITE_ON_BLACK

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Make this default y on various SoCs]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/rpi_defconfig b/configs/rpi_defconfig
index 4a90ca8..a07d698 100644
--- a/configs/rpi_defconfig
+++ b/configs/rpi_defconfig
@@ -19,6 +19,7 @@
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y
 CONFIG_USB_KEYBOARD=y
+CONFIG_SYS_WHITE_ON_BLACK=y
 CONFIG_CONSOLE_SCROLL_LINES=10
 CONFIG_LCD=y
 CONFIG_PHYS_TO_BUS=y