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/arm/Makefile b/cmd/arm/Makefile
new file mode 100644
index 0000000..94367dc
--- /dev/null
+++ b/cmd/arm/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0+
+
+ifdef CONFIG_ARM64
+obj-$(CONFIG_CMD_EXCEPTION) += exception64.o
+else
+obj-$(CONFIG_CMD_EXCEPTION) += exception.o
+endif