scripts/build/elf_parser.py: make dependency graph output deterministic

Python's sets are not deterministic.

`devices` were already sorted but `dev_supports` is still a
non-deterministic set. Sort dev_supports to make the graph output
deterministic.

Fixes commit 29942475 ("scripts: gen_handles: output dependency graph")

It is quite ironic that this initial and non-deterministic graph commit
was concurrent with and slightly delayed other commit
f896fc23 ("scripts: gen_handles: Sort the device handles") which
fixed another, similar non-determinism issue in the same area. A true
"whack-a-mole"!

Signed-off-by: Marc Herbert <marc.herbert@intel.com>