clk: remove COMMON_CLK_DISABLE_UNUSED

Exposing this option generates confusion and incorrect behavior for
single-image builds across platforms.  Enable this behavior permanently.

Signed-off-by: Mike Turquette <mturquette@linaro.org>
Acked-by: Saravana Kannan <skannan@codeaurora.org>

diff --cc drivers/clk/Kconfig
Simple merge

diff --cc drivers/clk/clk.c
Simple merge