dt-bindings: clock: imx-lpcg: add support to parse clocks from device tree

MX8QM and MX8QXP LPCG Clocks are mostly the same except they may reside
in different subsystems across CPUs and also vary a bit on the availability.

Same as SCU clock, we want to move the clock definition into device tree
which can fully decouple the dependency of Clock ID definition from device
tree and make us be able to write a fully generic lpcg clock driver.

And we can also use the existence of clock nodes in device tree to address
the device and clock availability differences across different SoCs.

Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: devicetree@vger.kernel.org
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>