imx: Add support for i.MX28 based XEA board

This patch introduces support for i.MX28 based XEA board.

This board supports DM/DTS in U-Boot proper as well as DM aware drivers
in SPL (u-boot.sb) by using OF_PLATDATA.
More detailed information regarding usage of it can be found in
./board/liebherr/xea/README file.

U-Boot SPL 2019.10-rc1-00233-g6aa549f05c (Aug 12 2019 - 09:23:36 +0200)
Trying to boot from MMC1
MMC0: Command 8 timeout (status 0xf0344020)
mmc_load_image_raw_sector: mmc block read error

U-Boot 2019.10-rc1-00233-g6aa549f05c (Aug 12 2019 - 09:23:36 +0200)

CPU:   Freescale i.MX28 rev1.2 at 454 MHz
BOOT:  SSP SPI #3, master, 3V3 NOR
Model: Liebherr (LWE) XEA i.MX28 Board
DRAM:  128 MiB
MMC:   MXS MMC: 0
Loading Environment from SPI Flash... SF: Detected n25q128a13 with page size 256 Bytes, erase size 64 KiB, total 16 MiB
OK
In:    serial
Out:   serial
Err:   serial
Net:
Warning: ethernet@800f0000 (eth0) using random MAC address - ce:e1:9e:46:f3:a2
eth0: ethernet@800f0000
Hit any key to stop autoboot:  0

Signed-off-by: Lukasz Majewski <lukma@denx.de>
diff --git a/arch/arm/mach-imx/mxs/Kconfig b/arch/arm/mach-imx/mxs/Kconfig
index 68072d5..b90d7b6 100644
--- a/arch/arm/mach-imx/mxs/Kconfig
+++ b/arch/arm/mach-imx/mxs/Kconfig
@@ -60,6 +60,9 @@
 config TARGET_TS4600
 	bool "Support TS4600"
 
+config TARGET_XEA
+	bool "Support XEA"
+
 endchoice
 
 config SYS_SOC
@@ -67,6 +70,7 @@
 
 source "board/bluegiga/apx4devkit/Kconfig"
 source "board/freescale/mx28evk/Kconfig"
+source "board/liebherr/xea/Kconfig"
 source "board/ppcag/bg0900/Kconfig"
 source "board/schulercontrol/sc_sps_1/Kconfig"
 source "board/technologic/ts4600/Kconfig"