target-arm: Add AArch32 banked register access to secure physical timer

If EL3 is AArch32, then the secure physical timer is accessed via
banking of the registers used for the non-secure physical timer.
Implement this banking.

Note that the access controls for the AArch32 banked registers
remain the same as the physical-timer checks; they are not the
same as the controls on the AArch64 secure timer registers.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1437047249-2357-3-git-send-email-peter.maydell@linaro.org
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
