broadwell: enable PCIe endpoint CLK power management

BUG=chrome-os-partner:31424
BRANCH=none
TEST=build only, due to I don't have broadwell system with wifi to test
     need somebody help me to verify
Change-Id: I52360176e135ea7f01cc67a926be4870265f57d1
Signed-off-by: Kane Chen <kane.chen@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/220743
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/8448
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/soc/intel/broadwell/Kconfig

@@ -35,6 +35,7 @@ config CPU_SPECIFIC_OPTIONS
 	select PARALLEL_MP
 	select PCIEXP_ASPM
 	select PCIEXP_COMMON_CLOCK
+	select PCIEXP_CLK_PM
 	select SMM_MODULES
 	select SMM_TSEG
 	select SMP