Add PSA crypto module

New module psa_crypto.c (MBEDTLS_PSA_CRYPTO_C):
Platform Security Architecture compatibility layer on top of
libmedcrypto.

Implement psa_crypto_init function which sets up a RNG.

Add a mbedtls_psa_crypto_free function which deinitializes the
library.

Define a first batch of error codes.
diff --git a/visualc/VS2010/mbedTLS.vcxproj b/visualc/VS2010/mbedTLS.vcxproj
index 73c92bd..2c569e5 100644
--- a/visualc/VS2010/mbedTLS.vcxproj
+++ b/visualc/VS2010/mbedTLS.vcxproj
@@ -224,6 +224,9 @@
     <ClInclude Include="..\..\include\mbedtls\x509_crt.h" />

     <ClInclude Include="..\..\include\mbedtls\x509_csr.h" />

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

+    <ClInclude Include="..\..\include\psa\crypto.h" />

+    <ClInclude Include="..\..\include\psa\crypto_platform.h" />

+    <ClInclude Include="..\..\include\psa\crypto_extra.h" />

   </ItemGroup>

   <ItemGroup>

     <ClCompile Include="..\..\library\aes.c" />

@@ -281,6 +284,7 @@
     <ClCompile Include="..\..\library\platform_util.c" />

     <ClCompile Include="..\..\library\poly1305.c" />

     <ClCompile Include="..\..\library\ripemd160.c" />

+    <ClCompile Include="..\..\library\psa_crypto.c" />

     <ClCompile Include="..\..\library\rsa.c" />

     <ClCompile Include="..\..\library\rsa_internal.c" />

     <ClCompile Include="..\..\library\sha1.c" />