Add a comment explaining what this function does and where the values
come from.
If the architecture isn't know, instead of returning an empty string
which could fail mysteriously, raise a KeyError so it fails quickly.
(From OE-Core rev: 025414c16319b068df1cd757ad9a3c987a6b871d)
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>