CONFIG_64BIT_CONTEXT is not available for thedefaultarchitecture x86.
Result is shown for architecture mips
default or selected kernelversion does not have config value CONFIG_64BIT_CONTEXT.
Result is shown for kernelversion 5.13-rc2

Save 64bit integer registers

configname: CONFIG_64BIT_CONTEXT

Linux/MIPS Kernel Configuration
└─>Kernel type
└─>Save 64bit integer registers
In linux kernel since version 2.6.23 (release Date: 2007-10-09)  
Loongson2 CPU is 64bit , when used in 32BIT mode, its integer
registers can still be accessed as 64bit, mainly for multimedia
instructions. We must have all 64bit save/restored to make sure
those instructions to get correct result.