default or selected kernelversion does not have config value CONFIG_BLK_DEV_IDE_PMAC_ATA100FIRST.
Result is shown for kernelversion 6.9.9

Probe on-board ATA/100 (Kauai) first

configname: CONFIG_BLK_DEV_IDE_PMAC_ATA100FIRST

Linux Kernel Configuration
└─>Device Drivers
└─>ATA/ATAPI/MFM/RLL support (DEPRECATED)
└─>Probe on-board ATA/100 (Kauai) first
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
This option will cause the ATA/100 controller found in UniNorth2
based machines (Windtunnel PowerMac, Aluminium PowerBooks, ...)
to be probed before the ATA/66 and ATA/33 controllers. Without
these, those machine used to have the hard disk on hdc and the
CD-ROM on hda. This option changes this to more natural hda for
hard disk and hdc for CD-ROM.