sstatesig: Improve to handle locking of multiple machines

sstatesig: Improve to handle locking of multiple machines

Instead of a single monolithic SIGGEN_LOCKEDSIGS, split this into
separate variables, one per sstate package architecture. Add in
a new SIGGEN_LOCKEDSIGS_TYPES variable which lists the package
architectures to load in.

SIGGEN_LOCKEDSIGS_TYPES is made machine specific using overrides.

Also sort the hashes in the lists by PN to make diffing them easier.

(From OE-Core rev: d8b0ce35981931a39e7db9d8e78de6e009b34688)

(From OE-Core rev: b42f305ce38b9e0f1a2b7cb9586bbabcd2d27429)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>