PM: Fix freezer compilation if PM_SLEEP is unset

Freezer fails to compile if with the following configuration
settings:

CONFIG_CGROUPS=y
CONFIG_CGROUP_FREEZER=y
CONFIG_MODULES=y
CONFIG_FREEZER=y
CONFIG_PM=y
CONFIG_PM_SLEEP=n

Fix this by making process.o compilation depend on CONFIG_FREEZER.

Reported-by: Cheng Renquan <crquan@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Len Brown <len.brown@intel.com>

kernel/power/Makefile

@@ -4,7 +4,8 @@ EXTRA_CFLAGS	+=	-DDEBUG
 endif
 
 obj-y				:= main.o
-obj-$(CONFIG_PM_SLEEP)		+= process.o console.o
+obj-$(CONFIG_PM_SLEEP)		+= console.o
+obj-$(CONFIG_FREEZER)		+= process.o
 obj-$(CONFIG_HIBERNATION)	+= swsusp.o disk.o snapshot.o swap.o user.o
 
 obj-$(CONFIG_MAGIC_SYSRQ)	+= poweroff.o