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>

common/main.c

@@ -269,7 +269,9 @@ int abortboot(int bootdelay)
 /*
  * Return 0 on success, or != 0 on error.
  */
+#ifndef CONFIG_CMD_PXE
 static inline
+#endif
 int run_command2(const char *cmd, int flag)
 {
 #ifndef CONFIG_SYS_HUSH_PARSER