Currently for CONFIG_DM_VIDEO=y setting splashimage env variable doesn't
have any effect. Introduce a common function for both dm-video/lcd stacks,
that checks env("splashimage") and invokes bmp_display() accordingly.
For additional details please check discussion [1].

[1] https://lists.denx.de/pipermail/u-boot/2019-May/371002.html



Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>