sandbox: disable tracing before unmapping RAM

sandbox: disable tracing before unmapping RAM

Currently doing 'reset' command in sandbox with tracing enabled causes
SIGSEV

```
Hit any key to stop autoboot:  0
=>
=>
=> reset
resetting ...
Segmentation fault (core dumped)

```

Tracing callback uses RAM buffer for storing tracing reports, but
state_uninit() function unmaps whole RAM, which causes SIGSEV on umapped
memory inside tracing subsystem.

Fix it by disabling tracing before unmapping memory

Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Add missing check for CONFIG_TRACE:
Signed-off-by: Simon Glass <sjg@chromium.org>