CONFIG_SOC_TX4938 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_SOC_TX4938 (not configurable)

modulename: mem_tx4927.ko

and/or

pci-tx4938.ko

configname: CONFIG_SOC_TX4938

Linux Kernel Configuration
└─>SOC_TX4938
In linux kernel since version 2.6.27 (release Date: 2008-10-09)  
source code:
arch/mips/txx9/generic/

is selected by
CONFIG_BLK_DEV_IDE_TX4938