Guard against building _start symbol in .S files instead of conditional file compilation
Add additional sel4 entry point for chaining to a regular _start entry point
update for changes to vspace interface
Remove serial drivers; use drivers in libplatsupport instead
PC99: Remove EGA device; now lives in libplatsupport
respond to API change of libplatsupport character device
Support using the HPET with the IOAPIC in a limited fashion