target/arm: add support for 64-bit PMCCNTR in AArch32 mode

target/arm: add support for 64-bit PMCCNTR in AArch32 mode

In the PMUv3, a new AArch32 64-bit (MCRR/MRRC) accessor for the
PMCCNTR was added. In QEMU we forgot to implement this, so only
provide the 32-bit accessor. Since we have a 64-bit PMCCNTR
sysreg for AArch64, adding the 64-bit AArch32 version is easy.

We add the PMCCNTR to the v8_cp_reginfo because PMUv3 was added
in the ARMv8 architecture. This is consistent with how we
handle the existing PMCCNTR support, where we always implement
it for all v7 CPUs. This is arguably something we should
clean up so it is gated on ARM_FEATURE_PMU and/or an ID
register check for the relevant PMU version, but we should
do that as its own tidyup rather than being inconsistent between
this PMCCNTR accessor and the others.

Since the register name is the same as the 32-bit PMCCNTR, we set
ARM_CP_NO_GDB on the 32-bit one to avoid generating an invalid GDB XML.

See https://developer.arm.com/documentation/ddi0601/2024-06/AArch32-Registers/PMCCNTR--Performance-Monitors-Cycle-Count-Register?lang=en

Note for potential backporting:
 * this code in cpregs-pmu.c will be in helper.c on stable
   branches that don't have commit ae2086426d37

Cc: qemu-stable@nongnu.org
Signed-off-by: Alex Richardson <alexrichardson@google.com>
Message-id: 20250725170136.145116-1-alexrichardson@google.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>