Remove the cpu clock registration function and helpers. Replace
unnecessary configuration struct with static initialization of the
desired clock type.

Ninja rename a5_clk to cpu_clk to better align with cpufreq convention.
Tested-by: NKevin Hilman <khilman@baylibre.com>
Signed-off-by: NMichael Turquette <mturquette@baylibre.com>