OMAP4: clock data: Add control for pad_clks_ck and slimbus_clk
The gating of pad_clks and slimbus_ck is controlled by the PRCM, but
since the clock source is external, this is the SW responsability
to gate / un-gate it when the mcpdm or slimbus module need to be used.
There is no autogating possible with such external clock.
Add SW control to enable / disable this SW gating in the pad_clks_ck
and slimbus_clk clock node.