CONFIG_TUNE_Z990 is not available for thedefaultarchitecture x86.
Result is shown for architecture s390
default or selected kernelversion does not have config value CONFIG_TUNE_Z990.
Result is shown for kernelversion 6.9.9

IBM zSeries model z890 and z990

configname: CONFIG_TUNE_Z990

Tune code generation
└─>IBM zSeries model z890 and z990
In linux kernel since version 3.10 (release Date: 2013-06-30)  
depends
CONFIG_cc-option