bootcount: display5: spl: Extend DISPLAY5 board SPL to support bootcount checking

This patch is necessary for providing basic bootcount checking in the case
of using "falcon" boot mode in that board.

It forces u-boot proper boot, when we exceed the number of errors.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Stefan Roese <sr@denx.de>