ARM: ep93xx: Fix wait for UART FIFO to be empty

Commit 210dce5f "ARM: ep93xx: properly wait for UART FIFO to be empty"

Removed the timeout loop while waiting for the uart transmit fifo to
empty. Some bootloaders leave the uart in a state where there might
be bytes in the uart that are not transmitted when execution is handed
over to the kernel. This results in a deadlocked system while waiting
for the fifo to empty.

Add back the timeout wait to prevent the deadlock.

Increase the wait time to hopefully prevent the decompressor corruption
that lead to commit 210dce5f. This corruption was probably due to a
slow uart baudrate. The 10* increase in the wait time should be enough
for all cases.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Ryan Mallon <rmallon@gmail.com>