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/evb-rk3229_defconfig b/configs/evb-rk3229_defconfig
index f8ca1f6..33202e4 100644
--- a/configs/evb-rk3229_defconfig
+++ b/configs/evb-rk3229_defconfig
@@ -72,6 +72,7 @@
 CONFIG_TPL_RAM=y
 CONFIG_BAUDRATE=1500000
 CONFIG_DEBUG_UART_SHIFT=2
+CONFIG_SYS_NS16550_MEM32=y
 CONFIG_SYSRESET=y
 CONFIG_USB=y
 CONFIG_USB_GADGET=y