CONFIG_PPC_OF_BOOT_TRAMPOLINE is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

Support booting from Open Firmware or yaboot

configname: CONFIG_PPC_OF_BOOT_TRAMPOLINE

Linux Kernel Configuration
└─>Platform support
└─>Support booting from Open Firmware or yaboot
In linux kernel since version 2.6.30 (release Date: 2009-06-09)  
Support from booting from Open Firmware or yaboot using an
Open Firmware client interface. This enables the kernel to
communicate with open firmware to retrieve system information
such as the device tree.

In case of doubt, say Y