target/hppa: Fix PDC address translation on PA2.0 with PSW.W=0

target/hppa: Fix PDC address translation on PA2.0 with PSW.W=0

Fix the address translation for PDC space on PA2.0 if PSW.W=0.
Basically, for any address in the 32-bit PDC range from 0xf0000000 to
0xf1000000 keep the lower 32-bits and just set the upper 32-bits to
0xfffffff0.

This mapping fixes the emulated power button in PDC space for 32- and
64-bit machines and is how the physical C3700 machine seems to map
PDC.

Figures H-10 and H-11 in the parisc2.0 spec [1] show that the 32-bit
region will be mapped somewhere into a higher and bigger 64-bit PDC
space.  The start and end of this 64-bit space is defined by the
physical address bits. But the figures don't specifiy where exactly the
mapping will start inside that region. Tests on a real HP C3700
regarding the address of the power button indicate, that the lower
32-bits will stay the same though.
[1] https://parisc.wiki.kernel.org/images-parisc/7/73/Parisc2.0.pdf

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