target/hppa: Add diag instructions to set/restore shadow registers

target/hppa: Add diag instructions to set/restore shadow registers

The 32-bit PA-7300LC (PCX-L2) CPU and the 64-bit PA8700 (PCX-W2) CPU
use different diag instructions to save or restore the CPU registers
to/from the shadow registers.

Implement those per-CPU architecture diag instructions to fix those
parts of the HP ODE testcases (L2DIAG and WDIAG, section 1) which test
the shadow registers.

Signed-off-by: Helge Deller <deller@gmx.de>
[rth: Use decodetree to distinguish cases]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Helge Deller <deller@gmx.de>
Tested-by: Helge Deller <deller@gmx.de>