Spin loops in uart send functions

[krichardsson]

The uart1SendData() and uart2SendData() functions uses a spin loop to determine when the next byte can be pushed to the UART. Sending too much data continuously using these functions will block the task and is likely to cause starvation problems in the system.

Note: uart1Putchar() and uart2Putchar() are calling the send data functions and have the same problem

The suggested solution is to replace the spin loop with an interrupt and semaphore.

[knmcguire]

fixed by #1065