Create a common BR2_COPYTO to prepare to replace

all the different COPYTOs spread out all over
Buildroot.
Generate COPY_FILE subroutine which can be used
to copy a file.

$(COPY_FILE , file, directory, filename)
This will copy to binary dir and to the selected
copy dir if set in new config (intended to replace
all old COPYTO configs)

This is overridden by BUILDROOT_COPYTO,
if set into the environment.

docs/buildroot.html

@@ -247,6 +247,7 @@
     <li>HOSTCC</li>
     <li>UCLIBC_CONFIG_FILE=&lt;path/to/.config&gt;</li>
     <li>BUSYBOX_CONFIG_FILE=&lt;path/to/.config&gt;</li>
+    <li>BUILDROOT_COPYTO</li>
     <li>BUILDROOT_DL_DIR</li>
     <li>BUILDROOT_LOCAL</li>
     <li>BUILDROOT_USE_XWINDOWS</li>
@@ -264,6 +265,16 @@ $ make UCLIBC_CONFIG_FILE=uClibc.config BUSYBOX_CONFIG_FILE=$HOME/bb.config
 $ make HOSTCXX=g++-4.3-HEAD HOSTCC=gcc-4.3-HEAD
 </pre>
 
+    <p>If you want the result of your build to be copied to another directory
+    like /tftpboot for downloading to a board using tftp, then you
+    can use BUILDROOT_COPYTO to specify your location</p>
+    <p>Typically, this is set in your ~/.bashrc file
+
+<pre>
+$ export BUILDROOT_COPYTO=/tftpboot
+</pre>
+
+
     <h3><a name="helper_completion" id="helper_completion"></a>
     Using auto-completion</h3>