[bios] Add bin-x86_64-pcbios build platform

Move most arch/i386 files to arch/x86, and adjust the contents of the
Makefiles and the include/bits/*.h headers to reflect the new
locations.

This patch makes no substantive code changes, as can be seen using a
rename-aware diff (e.g. "git show -M5").

This patch does not make the pcbios platform functional for x86_64; it
merely allows it to compile without errors.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/interface/pcbios/bios_nap.c

@@ -0,0 +1,16 @@
+#include <ipxe/nap.h>
+#include <realmode.h>
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+/**
+ * Save power by halting the CPU until the next interrupt
+ *
+ */
+static void bios_cpu_nap ( void ) {
+	__asm__ __volatile__ ( "sti\n\t"
+			       "hlt\n\t"
+			       "cli\n\t" );
+}
+
+PROVIDE_NAP ( pcbios, cpu_nap, bios_cpu_nap );