image_types.bbclass: Make u-boot signed images more versatile
With the introduction of chaining compression/conversion support we can
convert the old image_types_uboot.bbclass code that did a hand-chaining
of a set of ${filesystem}.${compression} into generic and arbitrary
support to sign whatever the user wants to sign for their image.
This, for the record, does remove setting a valid compression type in
the record in favour of just saying none. This is not a generally
useful feature in U-Boot and I believe being versatile in terms of being
able to pass in arbitrary compressions is more important.
Signed-off-by: Tom Rini <trini@konsulko.com> Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
