arm/imx: fix AUTO_ZRELADDR selection

The AUTO_ZRELADDR selection for ARCH_IMX_V4_V5 and ARCH_MX5 should
really be mutually exclusive to ZBOOT_ROM just like what ARCH_IMX_V6_V7
does.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>