Fix potential deadlock in PL011 init function

Fix potential deadlock in PL011 init function

The PL011 initialization function disables the UART, flushes the FIFO
and waits for the current character to be transmitted before applying
the configuration and enabling the UART. This waiting might result in
a deadlock if the FIFO is disabled while another CPU is printing a
message since the flush of FIFO will never finish.

This patch fixes the problem by removing the flush operation and the
loop for last character completion from the initialization function.
The UART is disabled, configured and enabled again.

Change-Id: I1ca0b6bd9f352c12856f10f174a9f6eaca3ab4ea