host-xxd: new package

Signed-off-by: Ryan Barnett <rjbarnet@rockwellcollins.com>
uboot: introduce u-boot.pbl format

This commit introduces support for the u-boot.pbl image format. The
u-boot.pbl is a special U-Boot image that supports booting directly
from eSPI FLASH, SD/MMC and NAND, etc for Freescale's CoreNet SoC's.
These SoCs use PBL (Pre-Boot Loader) to load RCW (Reset Configuration
Word) and/or pre-initialization instructions (PBI). For more details
refer section 5 Pre-boot loader specifications of reference manual
P2040RM/P3041RM/P4080RM/P5020RM at link:

http://www.freescale.com/webapp/search/Serp.jsp?Reference+Manuals

In details, this commit:

 * Introduces the BR2_TARGET_UBOOT_FORMAT_PBL menuconfig option which
   will generate a u-boot.pbl image.

 * Allows customization of the PBL through the use of menuconfig
   options - BR2_TARGET_UBOOT_PBL_CUSTOM and it sub-options. The two
   file formats that are support for customizing these files are the
   '.cfg' format which is specified by docs/README.pblimage in the
   u-boot source - BR2_TARGET_UBOOT_PBL_CUSTOM_RCW_FILE and
   BR2_TARGET_UBOOT_PBL_CUSTOM_PBI_FILE -  and a 'Hex String' file
   which has been exported from  Freescales's Processor Expert tool
   (PE Tool) - BR2_TARGET_UBOOT_PBL_CUSTOM_PE_TOOL_FILE.

 * Allows for the generatation of an RCW.bin file that can be used
   with a u-boot.bin file for NOR based booting configuration. A
   custom PBL configuration must be specified via
   BR2_TARGET_UBOOT_PBL_CUSTOM_PE_TOOL_FILE

Signed-off-by: Ryan Barnett <rjbarnet@rockwellcollins.com>