board/seco: Add mx6q-uq7 basic board support

Add basic SECO MX6Q/uQ7 board support (Ethernet, UART, SD are supported).
It also adds a Kconfig skeleton to later add more SECO board (supporting
SoC and board variants).

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
diff --git a/arch/arm/cpu/armv7/mx6/Kconfig b/arch/arm/cpu/armv7/mx6/Kconfig
index a32fd87..076ba52 100644
--- a/arch/arm/cpu/armv7/mx6/Kconfig
+++ b/arch/arm/cpu/armv7/mx6/Kconfig
@@ -25,7 +25,18 @@
 config MX6SX
 	bool
 
+choice
+	prompt "MX6 board select"
+
+config TARGET_SECOMX6
+	bool "Support secomx6 boards"
+	select CPU_V7
+
+endchoice
+
 config SYS_SOC
 	default "mx6"
 
+source "board/seco/Kconfig"
+
 endif