dm: serial: use Driver Model for UniPhier serial driver

This commit converts UniPhier on-chip serial driver to driver model.

Since UniPhier SoCs do not have Device Tree support, some board files
should be added under arch/arm/cpu/armv7/uniphier/ph1-*/ directories.
(Device Tree support for UniPhier platform is still under way.)

Now the base address and master clock frequency are passed from
platform data, so CONFIG_SYS_UNIPHIER_SERIAL_BASE* and
CONFIG_SYS_UNIPHIER_UART_CLK should be removed.

Tested on UniPhier PH1-LD4 ref board.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>