ARM: S3C64XX: Add I2S clkdev support

I2S controller has an internal mux for RCLK source clks. The list
of source clk names were passed through platform data in non-dt case.
Register the existing RCLK source clocks with clkdev using generic
connection id. This is required as part of adding DT support
for I2S controller driver.

Signed-off-by: Padmavathi Venna <padma.v@samsung.com>
Acked-by: Sangbeom Kim <sbkim73@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>