Make the sysinit tool a build tool rather than building in with
/usr/bin/cc and running it from OBJDIR.
We don't need to define OBJCOPY.
Further simplify sysinit processing by adding kernel files to a KSRCS
variable.
Add SRI as a copyright holder due to large scale refactoring.
Split the makefile bits for Hans' kernel shim layer into their own
includable kshim.mk.
Move the kernel shim framework to its own directory.
Move the sysinit program to usr.bin and its header to kshim.
Moved a definition to the right place.
Move USB support into a .mk file so loaders can include it.
Convert usb support to use usbcore.mk and kshim.mk.