CONFIG_MXS_HAVE_PLATFORM_RTC_STMP3XXX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_MXS_HAVE_PLATFORM_RTC_STMP3XXX (not configurable)

modulename: platform-rtc-stmp3xxx.ko

configname: CONFIG_MXS_HAVE_PLATFORM_RTC_STMP3XXX

Linux Kernel Configuration
└─>MXS_HAVE_PLATFORM_RTC_STMP3XXX
In linux kernel since version 3.3 (release Date: 2012-03-18)  
source code:
arch/arm/mach-mxs/devices/platform-rtc-stmp3xxx.c