Convert CONFIG_SYS_NS16550_MEM32 et al to Kconfig

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>
diff --git a/configs/SBx81LIFKW_defconfig b/configs/SBx81LIFKW_defconfig
index 73ef73c..fa7c35b 100644
--- a/configs/SBx81LIFKW_defconfig
+++ b/configs/SBx81LIFKW_defconfig
@@ -63,7 +63,8 @@
 CONFIG_MII=y
 CONFIG_DM_RTC=y
 CONFIG_RTC_MV=y
-CONFIG_SYS_NS16550=y
+CONFIG_SYS_NS16550_SERIAL=y
+CONFIG_SYS_NS16550_REG_SIZE=-4
 CONFIG_SPI=y
 CONFIG_DM_SPI=y
 CONFIG_KIRKWOOD_SPI=y