ARM: S5P: Remove the unused clk_arm clock from plat-s5p

All the S5P series SoCs use the 'struct clksrc_clk' type to represent the
armclk. So the clk_arm clock instance available in the plat-s5p clock code
is not used in any of the S5P series SoCs.
This patch removes the unused clk_arm instance from plat-s5p clock code.

Reported-by: Jaecheol Lee <jc.lee@samsung.com>
Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>