serial: remove altera serial initializations

Both altera_jtag_serial_initialize() and
altera_serial_initialize() are no longer used after
they are converted to driver model.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Marek Vasut <marex@denx.de>