CONFIG_ARCH_MX25 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

MX25-based

modulename: clock-imx25.ko

configname: CONFIG_ARCH_MX25

Freescale CPU family:
└─>MX25-based
In linux kernel since version 2.6.32 (release Date: 2009-12-02)  
This enables support for systems based on the Freescale i.MX25 family

source code:
depends
 or CONFIG_ARCH_MXC


is depended by
CONFIG_SOC_IMX25