clk: tegra: Add flags to tegra_clk_periph()

We will need some tegra peripheral clocks with the CLK_IGNORE_UNUSED flag,
most notably mselect, which is a bridge between AXI and most peripherals.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>