Replace irq_enable() regions with explicit calls to check for irqs.

Replace irq_enable() regions with explicit calls to check for irqs.

Add new function yield() which will permit irqs to trigger.
The yield() call enables irqs to occur in 32bit mode.
Add [num]sleep calls that yield instead of just spinning.
Rename existing int 1586 usleep call to biosusleep.
Convert many calls to mdelay to msleep.