Add update cancellation callback

Author: sylane

src/grisp_updater_grisp2.erl

@@ -20,6 +20,7 @@
 -export([system_prepare_update/2]).
 -export([system_prepare_target/4]).
 -export([system_set_updated/2]).
+-export([system_cancel_update/1]).
 -export([system_validate/1]).
 -export([system_terminate/2]).
 
@@ -92,6 +93,9 @@ system_set_updated(#sys_state{boot = Boot, valid = 1} = State, 0)
 system_set_updated(#sys_state{boot = Boot, valid = Valid}, SysId) ->
     {error, {unexpected_update_state, {Boot, Valid, SysId}}}.
 
+system_cancel_update(#sys_state{valid = Valid} = State) ->
+    {ok, validate_update(State, Valid)}.
+
 system_validate(#sys_state{boot = SysId, update = SysId} = State) ->
     {ok, validate_update(State, SysId)};
 system_validate(#sys_state{update = UpdatSysId}) ->