CONFIG_OMAP_MBOX_FWK is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Mailbox framework support

modulename: mailbox_mach.ko

and/or

mailbox.ko

configname: CONFIG_OMAP_MBOX_FWK

Linux Kernel Configuration
└─>TI OMAP Common Features
└─>Mailbox framework support
In linux kernel since version 2.6.30 (release Date: 2009-06-09)  
Say Y here if you want to use OMAP Mailbox framework support for
DSP, IVA1.0 and IVA2 in OMAP1/2/3.

source code:
/arch/arm/mach-omap2/

is selected by
CONFIG_OMAP_REMOTEPROC

is depended by
CONFIG_TIDSPBRIDGE