imx: imx8mm_evk: enable CONFIG_DM_SERIAL

Enable CONFIG_DM_SERIAL. uart2 and its pinmux was already
marked with u-boot,dm-spl.

move the preloader_console_init() call after spl_early_init() to
avoid board hang

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/board/freescale/imx8mm_evk/spl.c b/board/freescale/imx8mm_evk/spl.c
index cf4882c..7eeec6c 100644
--- a/board/freescale/imx8mm_evk/spl.c
+++ b/board/freescale/imx8mm_evk/spl.c
@@ -72,14 +72,8 @@
 }
 #endif
 
-#define UART_PAD_CTRL	(PAD_CTL_DSE6 | PAD_CTL_FSEL1)
 #define WDOG_PAD_CTRL	(PAD_CTL_DSE6 | PAD_CTL_ODE | PAD_CTL_PUE | PAD_CTL_PE)
 
-static iomux_v3_cfg_t const uart_pads[] = {
-	IMX8MM_PAD_UART2_RXD_UART2_RX | MUX_PAD_CTRL(UART_PAD_CTRL),
-	IMX8MM_PAD_UART2_TXD_UART2_TX | MUX_PAD_CTRL(UART_PAD_CTRL),
-};
-
 static iomux_v3_cfg_t const wdog_pads[] = {
 	IMX8MM_PAD_GPIO1_IO02_WDOG1_WDOG_B  | MUX_PAD_CTRL(WDOG_PAD_CTRL),
 };
@@ -92,8 +86,6 @@
 
 	set_wdog_reset(wdog);
 
-	imx_iomux_v3_setup_multiple_pads(uart_pads, ARRAY_SIZE(uart_pads));
-
 	return 0;
 }
 
@@ -147,8 +139,6 @@
 
 	timer_init();
 
-	preloader_console_init();
-
 	/* Clear the BSS. */
 	memset(__bss_start, 0, __bss_end - __bss_start);
 
@@ -166,6 +156,8 @@
 		hang();
 	}
 
+	preloader_console_init();
+
 	enable_tzc380();
 
 	power_init_board();
diff --git a/configs/imx8mm_evk_defconfig b/configs/imx8mm_evk_defconfig
index 36bf17d..9ee157c 100644
--- a/configs/imx8mm_evk_defconfig
+++ b/configs/imx8mm_evk_defconfig
@@ -79,6 +79,7 @@
 CONFIG_DM_REGULATOR_FIXED=y
 CONFIG_DM_REGULATOR_GPIO=y
 CONFIG_DM_PWM=y
+CONFIG_DM_SERIAL=y
 CONFIG_PWM_IMX=y
 CONFIG_MXC_UART=y
 CONFIG_SYSRESET=y