pico-imx7d: Add SPL support

Convert pico-imx7d to SPL support.

There are two variants of pico-imx7d SOMs:
- One with 512MB of RAM
- One with 1GB of RAM

The 512MB module contains two Hynix H5TC2G63GFR-PBA.
The 1GB module contains two Hynix H5TC4G63GFR-PBA.

The RAM size is determined in runtime by reading GPIO1_12.

While at it, also add USB Serial Download mode support as it
is very helpful for loading SPL and u-boot.img via imx_usb_loader.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>

configs/pico-imx7d_defconfig

@@ -1,11 +1,22 @@
 CONFIG_ARM=y
 CONFIG_ARCH_MX7=y
 CONFIG_SYS_TEXT_BASE=0x87800000
+CONFIG_SPL_GPIO_SUPPORT=y
+CONFIG_SPL_LIBCOMMON_SUPPORT=y
+CONFIG_SPL_LIBGENERIC_SUPPORT=y
 CONFIG_TARGET_PICO_IMX7D=y
+CONFIG_SPL_MMC_SUPPORT=y
+CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL=y
+CONFIG_SPL_LIBDISK_SUPPORT=y
 CONFIG_IMX_RDC=y
 CONFIG_DISTRO_DEFAULTS=y
-CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/technexion/pico-imx7d/imximage.cfg"
+CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/mach-imx/spl_sd.cfg"
 CONFIG_BOOTCOMMAND="run finduuid; run distro_bootcmd"
+CONFIG_SPL_I2C_SUPPORT=y
+CONFIG_SPL_USB_HOST_SUPPORT=y
+CONFIG_SPL_USB_GADGET_SUPPORT=y
+CONFIG_SPL_USB_SDP_SUPPORT=y
 # CONFIG_CMD_BOOTD is not set
 # CONFIG_CMD_IMI is not set
 # CONFIG_CMD_XIMG is not set
@@ -15,6 +26,7 @@ CONFIG_CMD_GPT=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_USB=y
+CONFIG_CMD_USB_SDP=y
 CONFIG_CMD_USB_MASS_STORAGE=y
 # CONFIG_CMD_SETEXPR is not set
 # CONFIG_CMD_MII is not set