Add SD/MMC drivers of Realtek card readers for generic_x86_64 (#3170)

We added drivers for Realtek cards readers in #3005, however it also
needs MMC drivers in order to make card reading possible. Enable both
USB and PCI versions of those (each about ~40 kB).

Fixes #3167

buildroot-external/board/pc/generic-x86-64/kernel.config

@@ -43,6 +43,8 @@ CONFIG_MMC_BLOCK=y
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_ACPI=y
 CONFIG_MMC_SDHCI_PCI=y
+CONFIG_MMC_REALTEK_PCI=m
+CONFIG_MMC_REALTEK_USB=m
 CONFIG_X86_INTEL_LPSS=y
 
 CONFIG_MISC_RTSX_PCI=m