splash: display splash in DM_VIDEO configurations

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>

common/stdio.c

@@ -16,6 +16,7 @@
 #include <malloc.h>
 #include <stdio_dev.h>
 #include <serial.h>
+#include <splash.h>
 
 #if defined(CONFIG_SYS_I2C)
 #include <i2c.h>
@@ -366,6 +367,9 @@ int stdio_add_devices(void)
 	if (ret)
 		printf("%s: Video device failed (ret=%d)\n", __func__, ret);
 #endif /* !CONFIG_SYS_CONSOLE_IS_IN_ENV */
+#if defined(CONFIG_SPLASH_SCREEN) && defined(CONFIG_CMD_BMP)
+	splash_display();
+#endif /* CONFIG_SPLASH_SCREEN && CONFIG_CMD_BMP */
 #else
 # if defined(CONFIG_LCD)
 	drv_lcd_init ();