x86/aperfperf: Make it correct on 32bit and UP kernels

The utilization of arch_scale_freq_tick() for CPU frequency readouts is
incomplete as it failed to move the function prototype and the define
out of the CONFIG_SMP && CONFIG_X86_64 #ifdef.

Make them unconditionally available.

Fixes: bb6e89df ("x86/aperfmperf: Make parts of the frequency invariance code unconditional")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/202205010106.06xRBR2C-lkp@intel.com