Serial1 settings ignored on nano RP2040

Looks like the settings for Serial1 are ignored in mbed core for nano RP2040

Code example tested with a logic analyzer:

``` c++
void setup() {
Serial1.begin(115200, SERIAL_8E1); // 8bits, Even parity, 1 Stopbit
}

void loop() {
Serial1.write(0x0F);
delay(100);
}

```

Start by reproducing the Serial1.begin(115200, SERIAL_8E1) example on the nano RP2040 and inspect the Serial1 implementation and configuration path in the mbed core. Compare the logic-analyzer output with the requested 8 data bits, even parity, and 1 stop bit; done means those settings are applied to Serial1 while the example repeatedly transmits 0x0F.

Written by the indexing model from the issue text.