arch/arm64/imx9: Add SAR ADC support

[jihonen]

• Add support for the i.MX9 SAR ADC block.

The driver provides initialization, de-initialization, channel-mask validation, and one-shot reads for the supported ADC channels. It also handles ADC clock bring-up, power-up, calibration, and raw 12-bit result extraction from the per-channel data registers.

Summary

Add a basic helper driver for the i.MX9 SAR ADC block in arch/arm64/src/imx9.

This adds the low-level ADC bring-up and sampling path needed for board-level analog sampling on i.MX9 systems, so board code does not need to duplicate the register setup and conversion flow.

The driver:

• enables and disables the ADC clock tree through the i.MX9 CCM helpers
• powers up the ADC block
• runs the calibration sequence during initialization
• clears stale status before the first conversion
• starts one-shot conversions on a requested channel
• reads the raw 12-bit result from the per-channel data register
• reports initialization state for board code

Impact

This change adds new runtime support in arch/arm64/src/imx9 only.
Impact areas:

• Build: imx9_sar_adc.c is compiled when CONFIG_IMX9_SAR_ADC is enabled
• Runtime: adds ADC initialization, de-initialization, and read support for the i.MX9 SAR ADC block
• API: adds the internal helper interface in imx9_sar_adc.h for board/arch bring-up code
• Compatibility: no existing user-space API is changed
• Documentation: no documentation updates were included in this change
• Security: no security-sensitive behavior is introduced

Testing

Testing performed:

• Built and ran on i.MX 93 hardware
• Verified ADC reporting with listener adc_report

Observed output:

TOPIC: adc_report
  adc_report
    timestamp: 11804674 (0.001465 seconds ago)
    device_id: 9371904 (Type: 0x8F, UNKNOWN:0 (0x01))
    raw_data: [2024, 2032, 1355, 6, 0, 0, 0, 0, 0, 0, 0, 0]
    resolution: 4096
    v_ref: 1.80000
    channel_id: [0, 1, 2, 3, -1, -1, -1, -1, -1, -1, -1, -1]

References:

• nuttx: arch/arm64/src/imx9/imx9_sar_adc.c
• nuttx: arch/arm64/src/imx9/imx9_sar_adc.h

Dependencies:

• none

[acassis]

@jihonen Nice work! I noticed that iMX9 family is missing a landing page: https://nuttx.apache.org/docs/latest/platforms/arm64/imx9/index.html like other chips, i.e.: https://nuttx.apache.org/docs/latest/platforms/arm/s32k1xx/index.html

Could you please just add a "Supported Modules & Peripherals" there adding ADC as Yes ?