ARM: SAMSUNG: Move PWM device definition from plat-s3c24xx to plat-samsung

This patch does the following:-
1. It moves file pwm.c from plat-s3c24xx to plat-samsung. This will
   enable all machines with Samsung SoCs to make use of the same code.
2. The device definitions have been separated to a new file dev-pwm.c
   for better clarity and structure.
3. It will enable all Samsung S3C and S5P series SoC's to use common
   PWM Kconfig definition.

Signed-off-by: Banajit Goswami <banajit.g@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>