hw/arm_sysctl: Fix RESETCTL for realview-pb-a8 and -pbx-a9

Depending on the considered baseboard the bit used to
reset the platform is different.

Here is the list of considered Realview/Versatile platforms:

Realview/Versatile AB for ARM926EJ-S: BOARD_ID = 0x100 = BOARD_ID_PB9
http://infocenter.arm.com/help/topic/com.arm.doc.dui0225d/CACCIFGI.html

RealView Emulation Baseboard: BOARD_ID = 0x140 = BOARD_ID_EB
No reset register

RealView PB for Cortex-A8: BOARD_ID = 0x178 = BOARD_ID_PBA8
http://infocenter.arm.com/help/topic/com.arm.doc.dui0417d/BBACIGAD.html

RealView PB for Cortex-A9: BOARD_ID = 0x182 = BOARD_ID_PBX
http://infocenter.arm.com/help/topic/com.arm.doc.dui0440b/CACCHBFB.html



Motherboard Express =C2=B5ATX: BOARD_ID = 0x190 = BOARD_ID_VEXPRESS
No reset register

Signed-off-by: Jean-Christophe DUBOIS <jcd@tribudubois.net>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andrzej Zaborowski <andrew.zaborowski@intel.com>