CONFIG_MACH_RX1950 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

HP iPAQ rx1950

modulename: mach-rx1950.ko

configname: CONFIG_MACH_RX1950

Linux Kernel Configuration
└─>SAMSUNG S3C24XX SoCs Support
└─>HP iPAQ rx1950
In linux kernel since version 2.6.35 (release Date: 2010-08-01)  
Say Y here if you're using HP iPAQ rx1950

source code:
arch/arm/mach-s3c24xx/mach-rx1950.c