Kconfig: mx6ull: Deselect MX6UL from CONFIG_MX6ULL

MX6UL contains features that MX6ULL doesn't support.
Deselect CONFIG_MX6UL and select SYS_L2CACHE_OFF and ROM_UNIFIED_SECTIONS.

The motivation for doing this change is that MX6UL supports CAAM and
MX6ULL does not.
Signed-off-by: NBreno Lima <breno.lima@nxp.com>
Reviewed-by: NFabio Estevam <fabio.estevam@nxp.com>

arch/arm/mach-imx/mx6/Kconfig

@@ -66,8 +66,9 @@ config MX6UL_OPOS6UL
 	select SUPPORT_SPL
 
 config MX6ULL
+	select SYS_L2CACHE_OFF
+	select ROM_UNIFIED_SECTIONS
 	bool
-	select MX6UL
 
 config MX6_DDRCAL
 	bool "Include dynamic DDR calibration routines"