This moves the bulk of the geli support from lib386/biosdisk.c into a new geli/gelidev.c which implements a devsw-type device whose dv_strategy() function handles geli decryption. Support for all arches comes from moving the code to taste-and-attach to the devopen() function in libsa.
After opening any DEVT_DISK device, devopen() calls the new function geli_probe_and_attach(), which will "attach" the geli code to the open_file struct by creating a geli_devdesc instance to replace the disk_devdesc instance in the open_file. That routes all IO for the device through the geli code.
A new public geli_add_key() function is added, to allow arch/vendor-specific code to add keys obtained from custom hardware or other sources.
With these changes, geli support will be compiled into all variations of loader(8) on all arches because the default is WITH_LOADER_GELI. Is that an appropriate default for all arches?