Move object files to $(obj)/<class>/

Instead of tagging object files with .<class>, move them to a <class>
directory below $(obj)/. This way we can keep a 1:1 mapping between
source- and object-file names.

The 1:1 mapping is a prerequisite for Ada, where the compiler refuses
any other object-file name.

Tested by verifying that the resulting coreboot.rom files didn't change
for all of Jenkins' abuild configurations.

Change-Id: Idb7a8abec4ea0a37021d9fc24cc8583c4d3bf67c
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/13181
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
6 files changed