Rather than stuffing the command line with a bunch of -D flags, start
moving things to config.h which is managed by autoheader. This makes
the makefile a bit simpler and the build output tighter, and it makes
the migration to automake easier as there are fewer vars to juggle.
We'll want to move the other options out too, but it'll take more work.
The common subdir sets up a cconfig.h file to hold checks for the common
code. In practice, most files still end up using config.h instead which
just leads to confusion.
Merge all the configure checks that went into cconfig.h into SIM_AC_COMMON
so we can drop the cconfig.h file altogether. Now there is only a single
config.h file like normal.
No arch is using this anymore, and we want all new ports using the
hardware framework instead. Punt WITH_DEVICES and the two callbacks
device_io_{read,write}_buffer.
We can also punt the tconfig.h file as no port is using it anymore.
This fixes in-tree builds that get confused by picking up the wrong
one (common/ vs <port>/) caused by commit ae7d0cac8c.
Any port that needs to set up a global define can use their own
sim-main.h file that they must provide regardless.
