Makefile: Add subdir dependency on config-devices-all.mak

Makefile: Add subdir dependency on config-devices-all.mak

What 23bf49b5eca716aaad073f2b47613434e1515cb5 really seemed to try to
fix is that Makefile could recurse into *-softmmu/ subdirectories before
a new *-softmmu/config-devices.mak was generated from pci.mak.

Fix this by adding a dependency on config-all-devices.mak, which in turn
has dependencies on *-softmmu/config-devices.mak.

Reported-by: Gerhard Wiesinger <lists@wiesinger.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>