Convert CONFIG_LCD_DT_SIMPLEFB to Kconfig

This converts the following to Kconfig:
   CONFIG_LCD_DT_SIMPLEFB

This patch also renames this config to CONFIG_FDT_SIMPLEFB as the code in
common/lcd_simplefb.c support CONFIG_LCD and CONFIG_VIDEO.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Matthias Brugger <mbrugger@suse.com>
diff --git a/common/Kconfig b/common/Kconfig
index fede7e4..176fda9 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -776,3 +776,12 @@
 	  Enable image_sign_info helper functions in SPL.
 
 endif
+
+config FDT_SIMPLEFB
+	bool "FDT tools for simplefb support"
+	depends on OF_LIBFDT
+	help
+	  Enable the fdt tools to manage the simple fb nodes in device tree.
+	  These functions can be used by board to indicate to the OS
+	  the presence of the simple frame buffer with associated reserved
+	  memory