Add hack for raising oscillator startup delay

See merge request !10

We've found that a certain percentage of production bricks fails to
reliably start up. This was traced down to the communication between
RP2040 and the flash chip. Some initial SPI communication would happen,
but eventually the communication would cease.

Through trial-and-error, it was discovered that raising the oscillator
startup delay makes the issue disappear. This commit adds
a Pico SDK patch to alter the oscillator configuration in Pico SDK.

For now, this is intentionally done as a simple hack. In the long-term,
a proper patch adding OpenCube as a new board should be upstreamed either
to the Pico SDK or to MicroPython.

The previous solution did not actually apply the patch and so the bug was
not actually mitigated. Fix the issue to reduce the frequency of crashes.