ARM: Alpine: early-debug print support

Alpine platform includes UART8250 that can be used for early prints.

Signed-off-by: Saeed Bishara <saeed@annapurnalabs.com>
Signed-off-by: Tsahee Zidenberg <tsahee@annapurnalabs.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>