spl: Kconfig: Move SPL_DISPLAY_PRINT to Kconfig

Move this option to Kconfig and tidy up existing uses. Also add a function
comment to the header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/cpu/armv7/omap4/Kconfig b/arch/arm/cpu/armv7/omap4/Kconfig
index c3dc95f..2091dd7 100644
--- a/arch/arm/cpu/armv7/omap4/Kconfig
+++ b/arch/arm/cpu/armv7/omap4/Kconfig
@@ -33,6 +33,9 @@
 config SPL_SERIAL_SUPPORT
 	default y
 
+config SPL_DISPLAY_PRINT
+	default y
+
 choice
 	prompt "OMAP4 board select"
 	optional