ARM: uniphier: remove commented out define

ARM: uniphier: remove commented out define

This TODO is no longer useful.  CONFIG_SYS_NS16550_SERIAL is just
ignored on DM serial.

If one wants to use the 16550A UART device on the UniPhier Micro
Support Card, it can be enabled by CONFIG_SYS_NS16550 via Kconfig.
Please notice CONFIG_SPL_OF_TRANSLATE must be enabled as well and
the device tree must be treaked in order to use the NS16550 serial
on SPL.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>