arm64/topology: Populate arch_scale_thermal_pressure() for arm64 platforms

Hook up topology_get_thermal_pressure to arch_scale_thermal_pressure thus
enabling scheduler to retrieve instantaneous thermal pressure of a CPU.

Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200222005213.3873-5-thara.gopinath@linaro.org