ARM: SAMSUNG: Fix switching FIFO in arch_enable_uart_fifo function

When CONFIG_S3C_BOOT_UART_FORCE_FIFO symbol is set, we should
enable FIFO but actually switch command is missing in the code.
This patch adds this switching.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>