CONFIG_CONFIG_BLKDEV_RESERVE_ADDRESS is not available for thedefaultarchitecture x86.
Result is shown for architecture h8300
default or selected kernelversion does not have config value CONFIG_CONFIG_BLKDEV_RESERVE_ADDRESS.
Result is shown for kernelversion 5.4.123

start address

configname: CONFIG_CONFIG_BLKDEV_RESERVE_ADDRESS

Linux Kernel Configuration
└─>Kernel hacking
└─>start address
In linux kernel since version 2.6.12  
BLKDEV start address.