uboot-phytec

arm: vf610: lpuart: disable FIFO on initializaton

UART does not use the UART FIFO, but we should also not rely that
the UART FIFO is diabled by default. For instance, when loading
U-Boot using the boot ROMs serial downloader protocol over UART,
FIFO is enabled at U-Boot start time.

This patch disables the RX and TX FIFO, sets back their thresholds
and flushes them.

Signed-off-by: Stefan Agner <stefan@agner.ch>