sencha: fix sw revoker shadow config

The shadow bitmmap used by the software revoker was overlapping
instruction memory and was too small to track the heap. Note this assumes
the simulation configures the extra memory.

Bypass-Presubmit-Reason: no test coverage

Change-Id: Iacf0122e1169f80be51e01f34b36f9c670afa630

sdk/boards/sencha.json

diff --git a/sdk/boards/sencha.json b/sdk/boards/sencha.json
index 92912ce..c70a59e 100644
--- a/sdk/boards/sencha.json
+++ b/sdk/boards/sencha.json
@@ -29,8 +29,8 @@
             "length": 0x40
         },
         "shadow" : {
-            "start": 0x50077000,
-            "end":   0x50078000
+            "start": 0x50080000,
+            "length": 0x2000
         }
     },
     "instruction_memory": {
@@ -39,7 +39,7 @@
     },
     "heap": {
         "start": 0x50078000,
-        "end":   0x50080000
+        "end": 0x50080000
     },
     "interrupts": [
         {