Incorrect implementatios of portENABLE_INTERRUPTS.

[vmpru]

This port use incorrect implementatios of portENABLE_INTERRUPTS. Two consecutive calls of portENABLE_INTERRUPTS make interrupts disabled:

#define portENABLE_INTERRUPTS()		enh_alt_irq_enable_all()
void enh_alt_irq_enable_all()
{
	alt_irq_context restore = lastContext;
	lastContext = 0;
	alt_irq_enable_all(restore);
}