subr_firmware: implementing firmware_path kenv support

hi freebsd-hackers@

i'm looking into the TODO in sys/kern/subr_firmware.c ~line 288 which 
mentions
looping over a path list fetched from a firmware_path kenv that the 
loader sets.

after looking through the src, it looks like the loader doesn't set the 
kenv yet

would an implementation require a loader change in stand/ or have i 
misread
something?

also, before i start writing after the above has been clarified,
is this a desired feature?
what's the format for the path list? (colon seperated, or like commas or
sometihng else)?

thanks
-ben