imx: mx6ul_14x14_evk add basic board support

imx: mx6ul_14x14_evk add basic board support

1. Add USDHC, I2C, UART, 74LV, USB, QSPI support.
2. Support SPL
3. CONFIG_MX6UL_14X14_EVK_EMMC_REWORK is introduced, this board default
   supports sd for usdhc2, but can do hardware rework to make usdhc2 support
   emmc.

Boot Log:
U-Boot SPL 2015.07-rc3-00124-g35d727b (Jul 20 2015 - 18:40:59)
reading u-boot.img
reading u-boot.img

U-Boot 2015.07-rc3-00124-g35d727b (Jul 20 2015 - 18:40:59 +0800)

CPU:   Freescale i.MX6UL rev1.0 792 MHz (running at 396 MHz)
CPU:   Commercial temperature grade (0C to 95C)CPU:   Thermal invalid data, fuse: 0x0
 - invalid sensor device
 Reset cause: POR
 Board: MX6UL 14x14 EVK
 I2C:   ready
 DRAM:  512 MiB
 MMC:   FSL_SDHC: 0, FSL_SDHC: 1
 *** Warning - bad CRC, using default environment

 In:    serial
 Out:   serial
 Err:   serial
 Net:   CPU Net Initialization Failed
 No ethernet found.
 Hit any key to stop autoboot:  0

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>