video: tweak CONFIG_SPL_VIDEO description

Make it clear that this is the SPL option to avoid potential confusion
when the description for CONFIG_SPL_VIDEO is the same as that for
CONFIG_VIDEO.

Signed-off-by: John Keeping <john@metanate.com>
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index fcc0e85..1e2f4e6 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -962,7 +962,7 @@
 endif # VIDEO
 
 config SPL_VIDEO
-	bool "Enable driver model support for LCD/video"
+	bool "Enable driver model support for LCD/video in SPL"
 	depends on SPL_DM
 	help
 	  The video subsystem adds a small amount of overhead to the image.