CONFIG_MACH_MX50_RDP is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Support MX50 reference design platform

modulename: mach-mx50_rdp.ko

configname: CONFIG_MACH_MX50_RDP

Linux Kernel Configuration
└─>Support MX50 reference design platform
In linux kernel since version 2.6.38 (release Date: 2011-03-14)  
Include support for MX50 reference design platform (RDP) board. This
includes specific configurations for the board and its peripherals.

source code: