Move entropy_poll.h to library

`entropy_poll.h` is not supposed to be used by application code and
is therefore being made internal.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
diff --git a/visualc/VS2010/mbedTLS.vcxproj b/visualc/VS2010/mbedTLS.vcxproj
index 80a8cd1..7c083f7 100644
--- a/visualc/VS2010/mbedTLS.vcxproj
+++ b/visualc/VS2010/mbedTLS.vcxproj
@@ -168,7 +168,6 @@
     <ClInclude Include="..\..\include\mbedtls\ecjpake.h" />

     <ClInclude Include="..\..\include\mbedtls\ecp.h" />

     <ClInclude Include="..\..\include\mbedtls\entropy.h" />

-    <ClInclude Include="..\..\include\mbedtls\entropy_poll.h" />

     <ClInclude Include="..\..\include\mbedtls\error.h" />

     <ClInclude Include="..\..\include\mbedtls\gcm.h" />

     <ClInclude Include="..\..\include\mbedtls\hkdf.h" />

@@ -238,6 +237,7 @@
     <ClInclude Include="..\..\library\cipher_wrap.h" />

     <ClInclude Include="..\..\library\common.h" />

     <ClInclude Include="..\..\library\ecp_alt.h" />

+    <ClInclude Include="..\..\library\entropy_poll.h" />

     <ClInclude Include="..\..\library\md_wrap.h" />

     <ClInclude Include="..\..\library\padlock.h" />

     <ClInclude Include="..\..\library\pk_wrap.h" />