CONFIG_PMC_MSP_EMBEDDED_ROOTFS is not available for the selected architecture x86.
Result is shown for architecture mips

Root filesystem embedded in kernel image

configname: CONFIG_PMC_MSP_EMBEDDED_ROOTFS

Linux Kernel Configuration
└─>Options for PMC-Sierra MSP chipsets
└─>Root filesystem embedded in kernel image
In linux kernel since version 2.6.23 (release Date: 2007-10-09)
selects
CONFIG_MTD
CONFIG_MTD_BLOCK
CONFIG_MTD_PMC_MSP_RAMROOT
CONFIG_MTD_RAM

depends
CONFIG_PMC_MSP