ARM: S5P6440: Remove usage of clk_arm and add clk_armclk clock

The clk_arm clock is of type 'struct clk' whereas on S5P6440,
the arm clock is more suitable to be of type 'struct clksrc_clk'
(since arm clock is divided version of apll clock).

This patch modifies the following.

1. Removes the usage of clk_arm clock (defined in plat-s5p) and
   defines the new clock 'clk_armclk' of type 'struct clksrc_clk'.

2. Rearranges the assignment of clock rate for the fout_a/m/epll
   clocks. This will help in calculating the clock rate of fclk
   from clk_armclk clock and setup the clock rate for fout_m/epll
   for subsequent patches which depend on it.

3. Modifies the clock rate calculation of fclk to be based on
   the newly added clk_armclk clock.

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>