parisc/firmware: Fix F-extend for PDC addresses

When running with narrow firmware (64-bit kernel using a 32-bit
firmware), extend PDC addresses into the 0xfffffff0.00000000
region instead of the 0xf0f0f0f0.00000000 region.

This fixes the power button on the C3700 machine in qemu (64-bit CPU
with 32-bit firmware), and my assumption is that the previous code was
really never used (because most 64-bit machines have a 64-bit firmware),
or it just worked on very old machines because they may only decode
40-bit of virtual addresses.

Cc: stable@vger.kernel.org
Signed-off-by: Helge Deller <deller@gmx.de>