hw/hppa: Fix booting Linux kernel with initrd

hw/hppa: Fix booting Linux kernel with initrd

Commit 20f7b890173b ("hw/hppa: Reset vCPUs calling resettable_reset()")
broke booting the Linux kernel with initrd which may have been provided
on the command line. The problem is, that the mentioned commit zeroes
out initial registers which were preset with addresses for the Linux
kernel and initrd.

Fix it by adding proper variables which are set shortly before starting
the firmware.

Signed-off-by: Helge Deller <deller@gmx.de>
Fixes: 20f7b890173b ("hw/hppa: Reset vCPUs calling resettable_reset()")
Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>