clk: ti: move low-level access and init code under clock driver

clk: ti: move low-level access and init code under clock driver

With most of the clock code under clock driver already, the low-level
register access code, and the init code for the same, is no longer
needed outside the clock driver. Thus, these can be moved under clock
driver also.

Signed-off-by: Tero Kristo <t-kristo@ti.com>