powercap/intel_rapl: Fix domain detection

As only the low 32 bits of the RAPL_DOMAIN_REG_STATUS register
represents the energy counter, and the high 32 bits are reserved,
detect the existence of a RAPL domain by checking the low 32 bits only.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>