machine/esp32: add ADC driver (#5595)

* machine/esp32: add ADC driver

Implements ADC1 on the Xtensa ESP32: InitADC, Configure and Get for
GPIO36, GPIO37, GPIO38, GPIO39, GPIO32, GPIO33, GPIO34 and GPIO35
(channels 0-7). The ADC pins are not contiguous on this chip, so the
pin to channel mapping is a lookup rather than arithmetic as on the
ESP32-S3.

Conversions are driven by the RTC controller under software control,
and Get returns the 12-bit sample scaled to 0..65520 to match the
other ESP ADC drivers.

The analog pads are spread over three unrelated RTC_IO registers
(SENSOR_PADS, XTAL_32K_PAD and ADC_PAD), so pad setup is kept local to
this file rather than adding a PinAnalog mode to machine_esp32.go.
That keeps the change to a single file.

Values are raw and uncalibrated. Unlike the ESP32-C3, S3 and C6
drivers there is no eFuse or self-calibration step; accurate voltage
mapping should be done with a two-point calibration in user code.

ADC2 is not implemented. On the ESP32 it is shared with the Wi-Fi
radio and cannot be used reliably while the radio is active.

Tested on an ESP32 Coreboard V2 with a photoresistor divider on
GPIO36. Readings swept 5056..59824 over the light range, all eight
channels returned independent values, and an invalid pin returned an
error from Configure and 0 from Get.

Signed-off-by: zombieleet <osikwemhev@gmail.com>

* fix: use package level err definiition and return (uint32, bool) from adcRTCGPIO

---------

Signed-off-by: zombieleet <osikwemhev@gmail.com>

GNUmakefile

@@ -989,6 +989,8 @@ endif
 ifneq ($(XTENSA), 0)
 	$(TINYGO) build -size short -o test.bin -target=esp32-generic       examples/machinetest
 	@$(MD5SUM) test.bin
+	$(TINYGO) build -size short -o test.bin -target=esp32-coreboard-v2  examples/adc
+	@$(MD5SUM) test.bin
 	$(TINYGO) build -size short -o test.bin -target=esp32c3-generic     examples/machinetest
 	@$(MD5SUM) test.bin
 	$(TINYGO) build -size short -o test.bin -target=esp32s3-generic     examples/machinetest