cmd: add exception command

The 'exception' command allows to test exception handling.

This implementation supports ARM, x86, RISC-V and the following exceptions:
* 'breakpoint' - prefetch abort exception (ARM 32bit only)
* 'unaligned'  - data abort exception (ARM only)
* 'undefined'  - undefined instruction exception

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 2bdbfcb..5d1999e 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1433,6 +1433,12 @@
 	  particularly for managing boot parameters as  well as examining
 	  various EFI status for debugging.
 
+config CMD_EXCEPTION
+	bool "exception - raise exception"
+	depends on ARM || RISCV || X86
+	help
+	  Enable the 'exception' command which allows to raise an exception.
+
 config CMD_LED
 	bool "led"
 	depends on LED