uart8250: Move under drivers/uart

Change-Id: Ic65ffaaa092330ed68d891e4a09a8b86cdc04a3a
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/5236
Tested-by: build bot (Jenkins)
7 files changed