smp branch: bugfix for race condition on RP2040 (#431)

smp branch: bugfix for race condition on RP2040 (#431)

* Bugfix for race condition on RP2040 in vPortEnableInterrupts()

RP2040 SMP port: Since spin_unlock() re-enables interrupts, pxYieldSpinLock has to be updated first to avoid a possible race condition.

* Bugfix for invalid sanity checks on RP2040

RP2040 SMP port: Testing pxYieldSpinLock for NULL does not work reliable in these places, because another/new lock might already be set when configASSERT() is executed.