Add board support for hawkboard

The patch adds basic board support for TI's OMAP-L138 based
Hawkboard. This board is pretty similar to the da850 EVM. Support for
nand and network access is added in this version.

The following bootup procedure is used.

At reset, the Rom Boot Loader(RBL), initialises the ddr and the nand
controllers and copies the second stage bootloader(nand_spl) to
RAM. The secondary bootloader then copies u-boot from a predefined
location in the nand flash to the RAM, and passes control to the
u-boot image.

Three config options are supported
* hawkboard_config - Used to create the u-boot.bin. Tftp the
 u-boot.bin image to the RAM from u-boot, and flash to the nand flash
 at address 0xe0000.

* hawkboard_nand_config - Used to generate the secondary
 bootloader(nand_spl) image. This creates an elf file u-boot-spl
 under nand_spl/. Create an AIS signed image using this file, and
 flash it to the nand flash at address 0x20000. The ais file should
 fit in one block.

* hawkboard_uart_confi...