Exynos: Add peripherial id for pwm

Add peripherial id for pwm inorder to support
generic api to get the clk frequency

Test with command "sf probe 1:0; time sf read 40008000 0 1000".
Try with different numbers of bytes and see that sane values are obtained
Build and boot U-boot with this patch, backlight works properly.

Signed-off-by: Padmavathi Venna <padma.v@samsung.com>
Signed-off-by: Akshay Saraswat <akshay.s@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>

arch/arm/include/asm/arch-exynos/periph.h

@@ -61,6 +61,11 @@ enum periph_id {
 	PERIPH_ID_SPI3,
 	PERIPH_ID_SPI4,
 	PERIPH_ID_SDMMC4,
+	PERIPH_ID_PWM0,
+	PERIPH_ID_PWM1,
+	PERIPH_ID_PWM2,
+	PERIPH_ID_PWM3,
+	PERIPH_ID_PWM4,
 
 	PERIPH_ID_COUNT,
 	PERIPH_ID_NONE = -1,