Display a splash image at U-boot stage.

[kmaincent]

Load and display an image at U-boot stage.

[kmaincent]

Commands to be added to U-boot environment.

STM32MP> load mmc 0:6 ${loadaddr} image.bmp  
18244 bytes read in 163 ms (108.4 KiB/s)
STM32MP> bmp display ${loadaddr}