GetMsgType : Take from config

GetMsgType response is hardcoded and always return only control
message support. Read supported message types from config file
and reply in control message

Tested by sending GetMsgType and GetVersion from another EP
Default responses for GetMsgType and GetVersion for type 0
5, 0, 1, 0 and 4, 0, 4, 241, 240, 255, 0, 241, 241, 255, 0, 241, 242, 255, 0, 241, 243, 241, 0

After calling
busctl call au.com.codeconstruct.MCTP1 /au/com/codeconstruct/mctp1 au.com.codeconstruct.MCTP1 RegisterResponder yau 5 1 0xF1F2F3F4
Response for GetMsgType and GetVersion for type 5
5, 0, 2, 0, 5 and 4, 0, 1, 244, 243, 242, 241

Signed-off-by: Nidhin MS <nidhin.ms@intel.com>

Author: msnidhin

docs/mctpd.md

@@ -25,8 +25,39 @@ Service au.com.codeconstruct.MCTP1:
 
 ## Top-level object: `/au/com/codeconstruct/mctp1`
 
-This object serves as the global MCTP daemon namespace; it doesn't contain
-much at present, but hosts two trees of MCTP objects:
+This object serves as the global MCTP daemon namespace.
+It hosts `au.com.codeconstruct.MCTP1` dbus interface to modify mctp properties like
+supported message types.
+```
+NAME                                TYPE      SIGNATURE  RESULT/VALUE  FLAGS
+au.com.codeconstruct.MCTP1          interface -          -             -
+.RegisterResponder                  method    yau        -             -
+```
+
+#### `.RegisterResponder`: `yau`
+
+This method is used to add support for mctp message types other than control
+messages. Once called successfully subsequent response for get message type
+control command will include this new message type also. Also the versions
+passed to this method will be used to respond to get version control command.
+
+`RegisterResponder <msg type> <versions>`
+
+If message type is already registered then dbus call will fail
+
+`<msg type>` Message type defined in DSP0239
+
+`<versions>` Versions supported for this message type formatted as uint32 integers as
+specified in DSP0236
+
+Example for PLDM type with two versions:
+
+```shell
+busctl call au.com.codeconstruct.MCTP1 /au/com/codeconstruct/mctp1 \
+  au.com.codeconstruct.MCTP1 RegisterResponder yau 1 2 0xF1F2F3F4 0xF0F0F0F1
+```
+
+Also it hosts two trees of MCTP objects:
 
  * Interfaces: Local hardware transport bindings that connect us to a MCTP bus
  * Endpoints: MCTP endpoints that `mctpd` knows about, both remote and local