Rename CONFIG_PWM to CONFIG_PWM_S5P and move to Kconfig

We rename the S5P specific "CONFIG_PWM" to CONFIG_PWM_S5P and move it to
Kconfig.  Given the usage of CONFIG_PWM_NX, we have that select this new
symbol.

Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/board/friendlyarm/Kconfig b/board/friendlyarm/Kconfig
index f8f9cfd..fa04727 100644
--- a/board/friendlyarm/Kconfig
+++ b/board/friendlyarm/Kconfig
@@ -11,6 +11,7 @@
 
 config PWM_NX
 	bool "PWM"
+	select PWM_S5P
 	help
 	  This enables LCD-Backlight control via PWM.
 endchoice