imx: imx8m: add Kconfig entry for i.MX8MP

Add Kconfig entry for i.MX8MP

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/arch/arm/mach-imx/imx8m/Kconfig b/arch/arm/mach-imx/imx8m/Kconfig
index eb4a73b..251feb2 100644
--- a/arch/arm/mach-imx/imx8m/Kconfig
+++ b/arch/arm/mach-imx/imx8m/Kconfig
@@ -16,6 +16,10 @@
 	bool
 	select IMX8M
 
+config IMX8MP
+	bool
+	select IMX8M
+
 config SYS_SOC
 	default "imx8m"