Increase GPS FIFO Buffer Size for RP2040 (#4741)

As discovered and tested by @Mictronics, default Serial FIFO size
on the Pico is 32bytes, which is not enough for GPS messages.

This patch increases the Serial GPS FIFO buffer size to 256
for the RP2040 Architecture

fixes https://github.com/meshtastic/firmware/issues/3989

src/gps/GPS.h

@@ -102,7 +102,7 @@ class GPS : private concurrency::OSThread
 
   public:
     /** If !NULL we will use this serial port to construct our GPS */
-#if defined(RPI_PICO_WAVESHARE)
+#if defined(ARCH_RP2040)
     static SerialUART *_serial_gps;
 #else
     static HardwareSerial *_serial_gps;