CONFIG_BOARD_HAMMERHEAD is not available for thedefaultarchitecture x86.
Result is shown for architecture avr32
default or selected kernelversion does not have config value CONFIG_BOARD_HAMMERHEAD.
Result is shown for kernelversion 6.5.1

Hammerhead board

configname: CONFIG_BOARD_HAMMERHEAD

AVR32 board type
└─>Hammerhead board
In linux kernel since version 2.6.29 (release Date: 2009-03-23)  
The Hammerhead platform is built around an AVR32 32-bit microcontroller from Atmel.
It offers versatile peripherals, such as ethernet, usb device, usb host etc.

The board also incorporates a power supply and is a Power over Ethernet (PoE) Powered
Device (PD).

Additionally, a Cyclone III FPGA from Altera is integrated on the board. The FPGA is
mapped into the 32-bit AVR memory bus. The FPGA offers two DDR2 SDRAM interfaces, which
will cover even the most exceptional need of memory bandwidth. Together with the onboard
video decoder the board is ready for video processing.

For more information see: http://www.miromico.ch/index.php/hammerhead.html