powercap / RAPL: fix build dependency on iosf_mbi

RAPL on Atom depends on IOSF_MBI driver for setting
floor frequency. This patch adds explicit dependency on
CONFIG_IOSF_MB.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/powercap/Kconfig

@@ -17,7 +17,7 @@ if POWERCAP
 # Client driver configurations go here.
 config INTEL_RAPL
 	tristate "Intel RAPL Support"
-	depends on X86
+	depends on X86 && IOSF_MBI
 	default n
 	---help---
 	  This enables support for the Intel Running Average Power Limit (RAPL)