drivers: video: Kconfig: Add configs for enabling video at SPL

Add Kconfigs which enable the video driver and splash screen at SPL
stage only and not at u-boot proper. The existing Kconfigs from u-boot
proper were not used to make SPL splash screen independent to them.

Signed-off-by: Nikhil M Jain <n-jain1@ti.com>
Reviewed-by: Devarsh Thakkar <devarsht@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>