hw/char: Add emulation of Diva GSP PCI management boards

hw/char: Add emulation of Diva GSP PCI management boards

The Diva GSP ("Guardian Service Processor") PCI boards are Remote
Management cards for PA-RISC machines.  They come with built-in 16550A
UARTs for serial consoles and modem functionalities, as well as a
mailbox-like memory area for hardware auto-reboot functionality.

Latest generation HP PA-RISC server machines use those Diva cards
for console output.

Signed-off-by: Helge Deller <deller@gmx.de>