CONFIG_REALVIEW_DT is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_REALVIEW_DT.
Result is shown for kernelversion 5.4.33

Support RealView(R) Device Tree based boot

modulename: realview-dt.ko

and/or

irq-gic-realview.ko

configname: CONFIG_REALVIEW_DT

Linux Kernel Configuration
└─>ARM Ltd. RealView family
└─>Support RealView(R) Device Tree based boot
In linux kernel since version 3.19 (release Date: 2015-02-08)  
Include support for booting the ARM(R) RealView(R) evaluation
boards using a device tree machine description.

source code:
arch/arm/mach-realview/realview-dt.c