Add pxe command

Add pxe command, which is intended to mimic PXELINUX functionality.
'pxe get' uses tftp to retrieve a file based on UUID, MAC address or IP
address. 'pxe boot' interprets the contents of PXELINUX config like file
to boot using a specific initrd, kernel and kernel command line.

This patch also adds a README.pxe file - see it for more details on the
pxe command.

Signed-off-by: Jason Hobbs <jason.hobbs@calxeda.com>
diff --git a/include/common.h b/include/common.h
index 7950c8b..77a29c8 100644
--- a/include/common.h
+++ b/include/common.h
@@ -255,6 +255,9 @@
 /* common/main.c */
 void	main_loop	(void);
 int	run_command	(const char *cmd, int flag);
+#ifdef CONFIG_CMD_PXE
+int run_command2(const char *cmd, int flag);
+#endif
 int	readline	(const char *const prompt);
 int	readline_into_buffer	(const char *const prompt, char * buffer);
 int	parse_line (char *, char *[]);
@@ -285,6 +288,9 @@
 /* common/cmd_doc.c */
 void	doc_probe(unsigned long physadr);
 
+/* common/cmd_net.c */
+int do_tftpb(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[]);
+
 /* common/cmd_nvedit.c */
 int	env_init     (void);
 void	env_relocate (void);