clk: tegra: common periph_clk_enb_refcnt and clks

This patch makes periph_clk_enb_refcnt a global array, dynamically allocated
at boottime. It simplifies the macros somewhat and allows clocks common to
several Tegra SoCs to be defined in a separate files. Also the clks array
becomes global and dynamically allocated which allows the DT registration to
be moved to a generic funcion.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>