build: Respect fs_config when generating recovery ramdisk

Without the -d $(TARGET_OUT) option for mkbootfs, only the
compiled-in fs_config (from AOSP) is used for the generated
ramdisk image. Device-specific additions are ignored.

This is why AOSP sets this option for both the boot- and recovery
ramdisk [1]. However, the option was removed for the recovery ramdisk
in review.lineageos.org/c/LineageOS/android_build/+/222722

This causes device-specific fs_config additions to be ignored when
generating the recovery ramdisk, potentially setting the wrong
permissions.

[1]: android.googlesource.com/platform/build/+/refs/tags/android-9.0.0_r37/core/Makefile#1388

Change-Id: I0f77a49d8b2f08791e60b34ddbb6f3b32bc2f0bc