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/efi-x86_payload64_defconfig b/configs/efi-x86_payload64_defconfig
index 28aaff6..89e6d1f 100644
--- a/configs/efi-x86_payload64_defconfig
+++ b/configs/efi-x86_payload64_defconfig
@@ -52,6 +52,7 @@
 CONFIG_LBA48=y
 CONFIG_SYS_64BIT_LBA=y
 # CONFIG_PCI_PNP is not set
+CONFIG_SYS_NS16550_PORT_MAPPED=y
 # CONFIG_GZIP is not set
 CONFIG_EFI=y
 CONFIG_EFI_STUB=y