allwinner/a10: Fix baudrate calculation

UART input clock is platform dependent. Also account for possible
use of get_option() where baudrate is not compile-time constant.

Change-Id: Ie1c8789ef72430e43fc33bfa9ffb9f5346762439
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/5289
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
2 files changed