CONFIG_SOC_IMX28 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_SOC_IMX28 (not configurable)

modulename: clock-mx28.ko

configname: CONFIG_SOC_IMX28

Linux Kernel Configuration
└─>SOC_IMX28
In linux kernel since version 2.6.38 (release Date: 2011-03-14)  
source code:

depends
CONFIG_ARCH_MXS

is selected by
CONFIG_FEC

is depended by
CONFIG_ARCH_MXS