This converts the following to Kconfig:
CONFIG_SPL_NS16550_MIN_FUNCTIONS
CONFIG_SYS_NS16550_MEM32
CONFIG_SYS_NS16550_PORT_MAPPED
CONFIG_SYS_NS16550_REG_SIZE
CONFIG_SYS_NS16550_SERIAL
To do this we also introduce CONFIG_SPL_SYS_NS16550_SERIAL so that
platforms can enable the legacy driver here for SPL.
Signed-off-by: Tom Rini <trini@konsulko.com>