i2c: imx-lpi2c: Add runtime PM support for IRQ and clock management on i.MX8QXP/8QM

On i.MX8QXP/8QM SoCs, both the lvds/mipi and lvds/mipi-lpi2c power domains
must enter low-power mode during runtime suspend to achieve deep power
savings.

LPI2C resides in the lvds-lpi2c/mipi-lpi2c power domain, while its IRQ is
routed through an irqsteer located in the lvds/mipi power domain. The LPI2C
clock source comes from an LPCG within the lvds-lpi2c domain.

For example, the hierarchy for lvds0 and lvds0-lpi2c0 domains is:
┌───────────────────────┐
│ pm-domain : lvds0     │
│                       │
│    ┌──────────────┐   │
│    │   irqsteer   │   │
│    └───────▲──────┘   │
│            │irq       │
│            │          │
└────────────┼──────────┘
┌────────────┼──────────┐
│        ┌───┼───┐      │
│        │lpi2c0 │      │
│        └───┬───┘clk   │
│   ┌────────┼───────┐  │
│   │       LPCG     │  │
│   └────────────────┘  │
│pm-domain:lvds0-lpi2c0 │
└───────────────────────┘

To allow these domains to power down in system runtime suspend:

- All irqsteer clients must release IRQs.
- All LPCG clients must disable and unprepare clocks.

Thus, LPI2C must:

- Free its IRQ during runtime suspend and re-request it on resume.
- Disable and unprepare all clocks during runtime suspend and prepare
  and rne ble them on resume.

This enables the lvds/mipi domains to enter deep low-power mode,
significantly reducing power consumption compared to active mode.

Signed-off-by: Carlos Song <carlos.song@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20251125084718.2156168-1-carlos.song@nxp.com

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