sandbox: Rework how SDL is enabled / disabled

Given that we can use Kconfig logic directly to see if we have a program
available on the host or not, change from passing NO_SDL to instead
controlling CONFIG_SANDBOX_SDL in Kconfig directly. Introduce
CONFIG_HOST_HAS_SDL as the way to test for sdl2-config and default
CONFIG_SANDBOX_SDL on if we have that, or not.

Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index c841b99..f539977 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -622,7 +622,7 @@
 
 config VIDEO_SANDBOX_SDL
 	bool "Enable sandbox video console using SDL"
-	depends on SANDBOX
+	depends on SANDBOX_SDL
 	help
 	  When using sandbox you can enable an emulated LCD display which
 	  appears as an SDL (Simple DirectMedia Layer) window. This is a