[ARM] 4854/1: fix the load address of uImage for CONFIG_ZBOOT_ROM=y

U-Boot puts an image at the load address specified in the uImage
header before jumping to the entry point.

In the CONFIG_ZBOOT_ROM case ZBOOT_ROM_TEXT is the right load
address.

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>