lcd: implement a callback for splashimage

lcd: implement a callback for splashimage

On some architectures certain values of splashimage will lead to
a data abort exception.

Document the problem, and implement a callback for splashimage to
reject such values.

Cc: Anatolij Gustschin <[email protected]>
Cc: Wolfgang Denk <[email protected]>
Signed-off-by: Nikita Kiryanov <[email protected]>
Acked-by: Igor Grinberg <[email protected]>