ARM: imx6q_logic: Enable DM_SERIAL

In order to call preloader_console_init from board_init_f when
DM_SERIAL is enabled, it neesd to call spl_early_init() to get early access
to DM and device tree.

This patch calls spl_early_init just before preloader_console_init()
and enables DM_SERIAL and SPL_DM_SERIAL.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/configs/imx6q_logic_defconfig b/configs/imx6q_logic_defconfig
index ec14b8e..6125ee2 100644
--- a/configs/imx6q_logic_defconfig
+++ b/configs/imx6q_logic_defconfig
@@ -83,6 +83,7 @@
 CONFIG_DM_REGULATOR_PFUZE100=y
 CONFIG_DM_REGULATOR_FIXED=y
 CONFIG_DM_REGULATOR_GPIO=y
+CONFIG_DM_SERIAL=y
 CONFIG_MXC_UART=y
 CONFIG_USB=y
 CONFIG_DM_USB=y