target/arm: Create timers in realize, not init

target/arm: Create timers in realize, not init

The timer_new() function allocates memory; this means that
if we call it in the CPU's init method we would need
to provide an instance_finalize method to free it. Defer
the timer creation to the realize function instead.

This fixes a memory leak spotted by clang LeakSanitizer
when a CPU object is created for introspection.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20181204132952.2601-6-peter.maydell@linaro.org