hw/hppa: Move software power button address to page zero

Something appears to be off between the 64-bit CPU, the 32-bit PDC
(SeaBIOS-hppa firmware), and the 64-bit kernel in addressing the
power button address in high-mapped firmware memory.

Use a 32-bit value at PAGE0->pad0[4] instead.

Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

hw/hppa/machine.c

@@ -36,7 +36,8 @@
 
 #define MIN_SEABIOS_HPPA_VERSION 10 /* require at least this fw version */
 
-#define HPA_POWER_BUTTON (FIRMWARE_END - 0x10)
+/* Power button address at &PAGE0->pad[4] */
+#define HPA_POWER_BUTTON (0x40 + 4 * sizeof(uint32_t))
 
 #define enable_lasi_lan()       0