Automatic MODULE_ALIAS() for DMI match tables.

This makes modpost handle MODULE_DEVICE_TABLE(dmi, xxxx).

I had to change the string pointers in the match table to char arrays,
and picked a size of 79 bytes almost at random -- do we need to make it
bigger than that? I was a bit concerned about the 'bloat' this
introduces into the match tables, but they should all be __initdata so
it shouldn't matter too much.

(Actually, modpost does go through the relocations and look at most of
them; it wouldn't be impossible to make it handle string pointers -- but
doesn't seem to be worth the effort, since they're __initdata).

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>