socfpga: map uart into virtual address space so that early_printk() works

Early printk code needs UART to be mapped early during
boot. early_printk() is left there during the start-up; it is useful
as our emulators are fairly slow.

Signed-off-by: Pavel Machek <pavel@denx.de>
Acked-by: Dinh Nguyen <dinguyen@altera.com>
[olof: removed redundant newlines]
Signed-off-by: Olof Johansson <olof@lixom.net>