Header rearrangement.

I want to get to the point where any header in include/ reflects a
standard user-level header (e.g. a POSIX header), while everything that's
specific to gPXE lives in include/gpxe/.  Headers that reflect a Linux
header (e.g. if_ether.h) should also be in include/gpxe/, with the same
name as the Linux header and, preferably, the same names used for the
definitions.

src/drivers/net/epic100.c

@@ -5,7 +5,7 @@
 #define LINUX_OUT_MACROS
 
 #include "etherboot.h"
-#include "pci.h"
+#include <gpxe/pci.h>
 #include "nic.h"
 #include "timer.h"
 #include "console.h"