sched: walt: Fix cpu_capacity_orig stuck issue

thermal_cap() should return the capacity corresponding to the
maximum frequency allowed by the thermal on a given CPU. If thermal
driver did not notify the limits not even once, thermal_cap()
fallback to CPU's cpu_capacity_orig since thermal_cap_cpu[] is not
initialized. In this case, if cpu_capacity_orig is clipped via
cpufreq policy limits, it would stuck there, even after the policy
limits are restored. Fix this issue by returning SCHED_CAPACITY_SCALE
as the capacity when thermal_cap_cpu[] is not initialized. The
cpu_capacity_orig is limited by arch_scale_cpu_capacity().

Change-Id: Ic0dda6ef28973ecf4e908df8c12e30585e320bf4
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>