Split the (quick hack) boot logic out from main.c to autoboot.c, add a

"boot" command to attempt booting from within the command shell, fall back
to shell if boot fails for any reason.

src/hci/commands/boot_cmd.c

@@ -0,0 +1,21 @@
+#include <vsprintf.h>
+#include <gpxe/command.h>
+#include <gpxe/autoboot.h>
+
+static int boot_exec ( int argc, char **argv ) {
+
+	if ( argc != 1 ) {
+		printf ( "Usage: %s\n"
+			 "Attempts to boot the system\n", argv[0] );
+		return 1;
+	}
+
+	autoboot();
+
+	return 0;
+}
+
+struct command boot_command __command = {
+	.name = "boot",
+	.exec = boot_exec,
+};