pico-imx7d: Provide a way to escape the Falcon mode

When CONFIG_SPL_OS_BOOT is selected, it is still convenient to be able
to escape from Falcon mode and boot to U-Boot proper.

Add a mechanism that allows booting in U-Boot proper when the
key 'c' is entered on console at boot time.
Signed-off-by: NFabio Estevam <festevam@gmail.com>
Signed-off-by: NOtavio Salvador <otavio@ossystems.com.br>

board/technexion/pico-imx7d/spl.c

@@ -21,6 +21,10 @@
 #ifdef CONFIG_SPL_OS_BOOT
 int spl_start_uboot(void)
 {
+	/* Break into full U-Boot on 'c' */
+	if (serial_tstc() && serial_getc() == 'c')
+		return 1;
+
 	return 0;
 }
 #endif