target/arm/cpu: Use ARRAY_SIZE() to iterate over ARMCPUInfo[]

target/arm/cpu: Use ARRAY_SIZE() to iterate over ARMCPUInfo[]

Use ARRAY_SIZE() to iterate over ARMCPUInfo[].

Since on the aarch64-linux-user build, arm_cpus[] is empty, add
the cpu_count variable and only iterate when it is non-zero.

Suggested-by: Richard Henderson <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Message-id: 20200504172448[email protected]
Signed-off-by: Peter Maydell <[email protected]>