default or selected kernelversion does not have config value CONFIG_MMC_SDHCI_OF.
Result is shown for kernelversion 5.6.18

SDHCI support on OpenFirmware platforms

modulename: sdhci-of.ko

configname: CONFIG_MMC_SDHCI_OF

Linux Kernel Configuration
└─>Device Drivers
└─>MMC/SD/SDIO card support
└─>SDHCI support on OpenFirmware platforms
In linux kernel since version 2.6.30 (release Date: 2009-06-09)  
This selects the OF support for Secure Digital Host Controller
Interfaces.

If unsure, say N.

source code:
drivers/mmc/host/