default or selected kernelversion does not have config value CONFIG_IR_RX51.
Result is shown for kernelversion 6.9.9

Nokia N900 IR transmitter diode

modulename: ir-rx51.ko

configname: CONFIG_IR_RX51

Linux Kernel Configuration
└─>Device Drivers
└─>Remote Controller support
└─>Remote Controller devices
└─>Nokia N900 IR transmitter diode
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Say Y or M here if you want to enable support for the IR
transmitter diode built in the Nokia N900 (RX51) device.

The driver uses omap DM timers for generating the carrier
wave and pulses.

source code:
drivers/media/rc/ir-rx51.c