sim/config:nexus-debug: correct memory size

A debug nexus build has 64M of SMC RAM, regardless of the real hardware
(debug builds can only run on Renode where memory is free!).

Change-Id: I672a683a1946dd67f2c188f81bbb0084bcc6d27f

platforms/nexus-debug.repl

diff --git a/platforms/nexus-debug.repl b/platforms/nexus-debug.repl
index ae7578c..6428069 100644
--- a/platforms/nexus-debug.repl
+++ b/platforms/nexus-debug.repl
@@ -8,6 +8,9 @@
 ram_sec:
     size: 0x01000000
 
+ram_smc:
+    size: 0x04000000
+
 // eFLASH            [‘h2000_0000 - ‘h20FF_FFFF)  16MB eFlash for Security Core (debugging size)
 eflash:
     size: 0x01000000