Fixes compilation because the Hal(Private)DispatchTable's, defined in
the bootloader's NTOS stub, are not external imports, as they would be
for a standard HAL.
- Rename UP -> PIC. The "up" folder in fact contains the code for
managing the Intel 8259 PIC chip
- Move amd64/processor.c -> apic/processor.c. The code is not tied to
amd64
- Remove platform from "halinit*" files. They already reside in the
corresponding folder