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/socfpga_chameleonv3_defconfig b/configs/socfpga_chameleonv3_defconfig
index 478efc5..00c4cf3 100644
--- a/configs/socfpga_chameleonv3_defconfig
+++ b/configs/socfpga_chameleonv3_defconfig
@@ -29,6 +29,7 @@
 CONFIG_SPL_FS_LOADER=y
 CONFIG_MMC_DW=y
 CONFIG_ETH_DESIGNWARE=y
+CONFIG_SYS_NS16550_MEM32=y
 CONFIG_TIMER=y
 CONFIG_SPL_TIMER=y
 CONFIG_DESIGNWARE_APB_TIMER=y