intel_rapl: abstract register access operations

MSR and MMIO RAPL interfaces have different ways to access the registers,
thus in order to abstract the register access operations, two callbacks,
.read_raw()/.write_raw() are introduced, and they should be implemented by
MSR RAPL and MMIO RAPL interface driver respectly.

This patch implements them for the MSR I/F only.

Reviewed-by: Pandruvada, Srinivas <srinivas.pandruvada@intel.com>
Tested-by: Pandruvada, Srinivas <srinivas.pandruvada@intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>