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The Nomadik clock implementation was a stub just using
fixed clocks.

This implements the clocks properly instead of relying
on them all being on at boot and leaving them all on.

The PLLs are on the top locking to the main chrystal
oscillator, then the HCLK for the peripherals are
below PLL2.

The gated clocks are implemented with zero cells and
given the clock ID as a property of each node, so every
gate need to have its own node in the device tree.
This is because the gate registers contain both HCLK
gates and PCLK gates, where the latter has HCLK as
parent. As can be seen from the register layout, this
is a complete mixup, which means all these gates need
their own node to properly model parent/child relations
for PCLKs apart from the HCLKs.

This driver also adds a helpful debugfs file to inspect
the hardware state of the clock gates.

This is the end result in <debugfs>/clk/clk_summary
after applying a proper device tree:

ulpiclk                0 ...