PM / devfreq: Move exynos4 devfreq driver into a new sub-directory

In anticipation of the new exynos5 devfreq and ppmu driver, create
an exynos sub-directory. Move the existing exynos4 devfreq driver
into the same.

Signed-off-by: Abhilash Kesavan <[e-mail]>
Acked-by: MyungJoo Ham <[e-mail]>
Cc: Jonghwan Choi <[e-mail]>
Cc: Kukjin Kim <[e-mail]>

drivers/devfreq/Makefile

···
 obj-$(CONFIG_DEVFREQ_GOV_USERSPACE)	+= governor_userspace.o
 
 # DEVFREQ Drivers
-obj-$(CONFIG_ARM_EXYNOS4_BUS_DEVFREQ)	+= exynos4_bus.o
+obj-$(CONFIG_ARM_EXYNOS4_BUS_DEVFREQ)	+= exynos/

drivers/devfreq/exynos/Makefile

···
+# Exynos DEVFREQ Drivers
+obj-$(CONFIG_ARM_EXYNOS4_BUS_DEVFREQ)	+= exynos4_bus.o