CONFIG_MACH_SEABOARD is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_MACH_SEABOARD.
Result is shown for kernelversion 6.2.5

Seaboard board

modulename: board-seaboard.ko

and/or

board-seaboard-pinmux.ko

configname: CONFIG_MACH_SEABOARD

Linux Kernel Configuration
└─>Seaboard board
In linux kernel since version 2.6.39 (release Date: 2011-05-18)  
Support for nVidia Seaboard development platform. It will
also be included for some of the derivative boards that
have large similarities with the seaboard design.

source code:
arch/arm/mach-tegra/board-seaboard.c