disas/hppa: implement mfdiag/mtdiag disassembly

The various PA-RISC CPUs implement different CPU-specific diag
instructions (mfdiag, mtdiag, mfcpu, mtcpu, ...) to access CPU-internal
diagnose/configuration registers, e.g. for cache control, managing space
register hashing, control front panel LEDs and read status of the
hardware reset button.

Those instructions are mostly undocumented, but are used by ODE, HP-UX
and Linux.

This patch adds some neccessary instructions for PCXL and PCXU CPUs.

Signed-off-by: Helge Deller <deller@gmx.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>