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

CONFIG_IMX_HAVE_PLATFORM_IMX_UART (not configurable)

modulename: platform-imx-uart.ko

configname: CONFIG_IMX_HAVE_PLATFORM_IMX_UART

Linux Kernel Configuration
└─>IMX_HAVE_PLATFORM_IMX_UART
In linux kernel since version 2.6.36 (release Date: 2010-10-20)  
source code:
arch/arm/plat-mxc/devices/platform-imx-uart.c