nios2: optionally print cause code reason

This is at the expense of code size. The QEMU and MAX10
targets have plenty of space so enable it for these boards,
but leave off by default for others.

Change-Id: I93fdb7db14232727e9953b22490d8869ff3b60e7
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>