sencha: correct CHERIoT software revoker setup

We (currently) do memory revocation in software on the SMC. Shrinking
SRAM to match the hardware resulted in the revokers's shadow bitmap
overlapping the heap. Grow memory owned by the CHERIoT cpu so we can
move the bitmap past the end of SRAM (this happens in the json board
description).  While here also disable the hardware revocation support.

Bypass-Presubmit-Reason: no test coverage

Change-Id: I12452283dee91e48d1ceae815c4ac318b2b377c3

platforms/sencha_smc.repl

diff --git a/platforms/sencha_smc.repl b/platforms/sencha_smc.repl
index 1acf7b1..f771519 100644
--- a/platforms/sencha_smc.repl
+++ b/platforms/sencha_smc.repl
@@ -22,9 +22,11 @@
     cpuType: "Mpact.Cheriot"
     endianness: Endianess.LittleEndian
     memoryBase: 0x50000000
-    memorySize: 0x80000
-    // XXX SWAG
-    revocationMemoryBase: 0x50070000
+    // Memory size includes 0x2000 for the shadow memory required for
+    // the software revoker. This assumes a max of 128KB is configured
+    // for the heap in the json board description.
+    memorySize: 0x82000
+    revocationMemoryBase: 0
     // Use the built-in clint to avoid update latency
     // NB: beware case, these are properties
     // NB: clint irq's are preset