boards: rp2040: set startup-delay-multiplier for applicable boards

This is based on boards in
https://github.com/raspberrypi/pico-sdk/tree/2.1.0/src/boards/include/boards


that have a custom value set for PICO_XOSC_STARTUP_DELAY_MULTIPLIER.

Signed-off-by: Xudong Zheng <7pkvm5aw@slicealias.com>