/etc/mach and 32-bit sd belong in system/kernel
Currently, as a historical accidental, the 32-bit sd driver (for i386) and the /etc/mach file are delivered by the driver/network/platform package. This is a historical accident resulting from the creation of that driver by a rename from the SUNWos86r package.
This makes this driver/network/platform package mandatory for x86 platforms, if that platform desires either a 32-bit disk support, or to have support for MP platforms (/etc/mach is used by MP platforms.)
The 32-bit sd driver (and the .conf file) should really be moved to system/kernel, and the /etc/mach component should move there as well.
This will leave only the legacy dnet driver in the driver/network/platform package (and presumably it would be a good idea to rename that package at some future date, perhaps to driver/network/dnet).