Compatibility with RP2350 when using RISC-V cores.

[JChristensen]

Library worked OK on RP2040 (Raspberry Pi Pico W) and RP2350 (Raspberry Pi Pico 2W) when using the ARM cores.
When using the RP2350 RISC-V cores, the compiler gave the following error:

sketchbook/libraries/Adafruit_SSD1306/Adafruit_SSD1306.cpp:54:10: fatal error: util/delay.h: No such file or directory
   54 | #include <util/delay.h>
      |          ^~~~~~~~~~~~~~
compilation terminated.
exit status 1
Error compiling for board Raspberry Pi Pico 2W.

Tested with Arduino 1.8.19 and the Arduino-Pico core 4.5.4.

[tyeth]

Looks good to me, tested with Arduino IDE 2.3.6 + Earle core 4.6.0, thanks for the contribution!