S5PC100: Moves the Macros to a common header file

The get_pll_clk(int) API returns the PLL frequency based on
the (int) argument which is defined locally in clock.c

Moving that #define to common header file (clk.h) would
be helpful when using the API from other files.

Signed-off-by: Naveen Krishna Ch <ch.naveen@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>