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/configs/secomx6quq7_defconfig b/configs/secomx6quq7_defconfig
new file mode 100644
index 0000000..dcd681d
--- /dev/null
+++ b/configs/secomx6quq7_defconfig
@@ -0,0 +1,7 @@
+CONFIG_SYS_EXTRA_OPTIONS="ENV_IS_IN_MMC"
+CONFIG_ARM=y
+CONFIG_ARCH_MX6=y
+CONFIG_TARGET_SECOMX6=y
+CONFIG_SECOMX6_UQ7=y
+CONFIG_SECOMX6Q=y
+CONFIG_SECOMX6_2GB=y