CONFIG_AT91_USE_OLD_CLK is not available for the selected architecture x86.
Result is shown for architecture arm

CONFIG_AT91_USE_OLD_CLK (not configurable)

configname: CONFIG_AT91_USE_OLD_CLK

Linux Kernel Configuration
└─>AT91_USE_OLD_CLK
In linux kernel since version 3.14 (release Date: 2014-03-30)