cmd: sandbox: implement exception command

Implement the commands

* exception undefined - execute an illegal instruction
* exception sigsegv - cause a segment violation

Here is a possible output:

    => exception undefined
    Illegal instruction
    pc = 0x55eb8d0a7575, pc_reloc = 0x57575
    Resetting ...

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 98cf543..c853ce7 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1691,7 +1691,7 @@
 
 config CMD_EXCEPTION
 	bool "exception - raise exception"
-	depends on ARM || RISCV || X86
+	depends on ARM || RISCV || SANDBOX || X86
 	help
 	  Enable the 'exception' command which allows to raise an exception.