gw_ventana: Use the generic spl_sd.cfg

gw_ventana can boot from SPI or NAND and both of these interfaces boot from
the same 0x400 offset.

This means that we could simplify the code and replace the custom gw_ventana.cfg
with the generic spl_sd.cfg, as it provides the same boot offset of 0x400.

Cc: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>

board/gateworks/gw_ventana/gw_ventana.cfg

-/*
- * Copyright (C) 2013 Gateworks Corporation
- *
- * SPDX-License-Identifier: GPL-2.0+
- *
- * Refer doc/README.imximage for more details about how-to configure
- * and create imximage boot image
- *
- * The syntax is taken as close as possible with the kwbimage
- */
-
-/* image version */
-IMAGE_VERSION 2
-
-/*
- * Boot Device : one of
- * spi, sd, nand, sata
- */
-#ifdef CONFIG_SPI_FLASH
-BOOT_FROM      spi
-#else
-BOOT_FROM      nand
-#endif

configs/gwventana_defconfig

 CONFIG_SPL=y
-CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/gateworks/gw_ventana/gw_ventana.cfg,MX6QDL"
+CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/imx-common/spl_sd.cfg,MX6QDL"
 +S:CONFIG_ARM=y
 +S:CONFIG_TARGET_GW_VENTANA=y