board: omapl138_lcdk: add the mmc device to SPL

We don't have full device-tree support in SPL yet - add an appropriate
U_BOOT_DEVICE() to the board file.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
diff --git a/board/davinci/da8xxevm/omapl138_lcdk.c b/board/davinci/da8xxevm/omapl138_lcdk.c
index d4cda0a..608a7f2 100644
--- a/board/davinci/da8xxevm/omapl138_lcdk.c
+++ b/board/davinci/da8xxevm/omapl138_lcdk.c
@@ -366,4 +366,13 @@
 	.name = "ns16550_serial",
 	.platdata = &serial_pdata,
 };
+
+U_BOOT_DEVICE(omapl138_mmc) = {
+	.name = "davinci_mmc",
+};
+
+void spl_board_init(void)
+{
+	davinci_configure_pin_mux(mmc0_pins, ARRAY_SIZE(mmc0_pins));
+}
 #endif