splash: Introduce default_splash_locations

splash: Introduce default_splash_locations

This change introduces default_splash_locations which
simplifies splash recovery from the first partition of
USB/MMC/SATA drive.

Given usual mapping of the first partition of external media for
basic boot stuff like uImage/zImage, .dtb etc it looks quite
obvious option to put there splash.bmp as well.

Signed-off-by: Alexey Brodkin <[email protected]>
Cc: Nikita Kiryanov <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Jeroen Hofstee <[email protected]>
Signed-off-by: Anatolij Gustschin <[email protected]>