target/arm: Ignore PMCR.D when PMCR.LC is set

The architecture requires that if PMCR.LC is set (for a 64-bit cycle
counter) then PMCR.D (which enables the clock divider so the counter
ticks every 64 cycles rather than every cycle) should be ignored.  We
were always honouring PMCR.D; fix the bug so we correctly ignore it
in this situation.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220822132358.3524971-5-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>