ARM: S5P6440: Change dout_mpll clock type to clksrc_clk clock type.

This patch modifies the following.

1. Modifies the dout_mpll clock type as clksrc_clk clock type.
   This modification allows the use of common clock code in
   managing the dout_mpll clock (which otherwise would need
   custom defined functions such as s5p6440_clk_doutmpll_get_rate).

2. s5p6440_clk_doutmpll_get_rate function is removed as it is
   no longer needed.

Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>