imx8: add hidden IMX8_ROMAPI Kconfig symbol

In order not to repeat the IMX8MN || IMX8MP || IMX8ULP logic in
multiple places where we need to know if the SOC exposes the ROM API,
add a "def_bool y" Kconfig symbol.

Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
diff --git a/arch/arm/mach-imx/Kconfig b/arch/arm/mach-imx/Kconfig
index ad0fb36..50f4c08 100644
--- a/arch/arm/mach-imx/Kconfig
+++ b/arch/arm/mach-imx/Kconfig
@@ -164,9 +164,13 @@
 	  shall perform it on a new PCB and then use those values to program
 	  the ddrmc_cr_setting on relevant board file.
 
+config IMX8_ROMAPI
+	def_bool y
+	depends on IMX8MN || IMX8MP || IMX8ULP
+
 config SPL_IMX_ROMAPI_LOADADDR
 	hex "Default load address to load image through ROM API"
-	depends on IMX8MN || IMX8MP || IMX8ULP
+	depends on IMX8_ROMAPI
 
 config IMX_DCD_ADDR
 	hex "DCD Blocks location on the image"