arm: Add const attribute to some arm_boot_info pointers

arm: Add const attribute to some arm_boot_info pointers

Parameter 'info' is const, so add the missing attribute.

v2:
Add 'const' to the local variable info in do_cpu_reset() and to
the boot_info field in CPUARMState (suggested by Peter Maydell).

Cc: Andrzej Zaborowski <balrogg@gmail.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Andrzej Zaborowski <andrew.zaborowski@intel.com>