`analogRead()` does not reset pin properly after previous `pinMode()`

BSP: Arduino MBed OS Giga boards v4.0.10
Board: Giga R1
Arduino IDE: 2.2.1

Sample sketch:
```c
void setup() {
Serial.begin(9600);
while (!Serial) { }

// Attach A0 to 3.3V through a 220K or other high-value resistor,
// so it's not stronger than the driven output.

delay(100);
Serial.println(analogRead(A0));

pinMode(A0, INPUT);

delay(100);
Serial.println(analogRead(A0));

Serial.println("Done");
}

void loop() {
}
```
On my test setup, this prints:
```
744
92
Done
```
I would expect it to print `744` or close to that twice.
Once the pin is used in the `pinMode()`, it appears to be pulled low.

By comparison, the same sketch on an Arduino Uno prints (with the 220K resistor connected to 5V):
```
1023
1023
Done
```

The use case is a resistive touch screen driver (https://github.com/adafruit/Adafruit_TouchScreen) which flips pins back and forth between digital input/output and analog input modes to read X/Y resistance values.

This is reminiscent of (though order is different) to https://github.com/arduino/ArduinoCore-mbed/issues/328 and https://github.com/arduino/ArduinoCore-renesas/issues/58

Start by running the provided sketch on a Giga R1 with Arduino MBed OS v4.0.10 and compare the readings before and after pinMode(A0, INPUT). Trace the pinMode() and analogRead() entry points for the board, then verify that the second reading remains close to the first and that the Adafruit_TouchScreen use case can switch pin modes correctly.

Written by the indexing model from the issue text.