target-arm: Implement AArch64 SPSR_EL1

target-arm: Implement AArch64 SPSR_EL1

Implement the AArch64 SPSR_EL1. For compatibility with how KVM
handles SPSRs and with the architectural mapping between AArch32
and AArch64, we put this in the banked_spsr[] array in the slot
that is used for SVC in AArch32. This means we need to extend the
array from uint32_t to uint64_t, which requires some reworking
of the 32 bit KVM save/restore code.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>