Create configuration option for restricted ns16550 functions

This patch will create a configuration option for a minimum configuration for
the ns16550 serial driver at drivers/serial/ns16550.c and will apply this new
configuration option to the SIMPC8313.h config file in order to fix the NAND
bootstrap build error.  This option will exclude all functions with exception of
NS16550_putc and NS16550_init.  This will be used primarily to save space and
remove unused code from builds in which space is limited.

Signed-off-by: Ron Madrid <ron_madrid@sbcglobal.net>
diff --git a/README b/README
index b64c159..48d3f6d 100644
--- a/README
+++ b/README
@@ -2458,6 +2458,13 @@
 - CONFIG_SYS_64BIT_STRTOUL:
 		Adds simple_strtoull that returns a 64bit value
 
+- CONFIG_NS16550_MIN_FUNCTIONS:
+		Define this if you desire to only have use of the NS16550_init
+		and NS16550_putc functions for the serial driver located at
+		drivers/serial/ns16550.c.  This option is useful for saving
+		space for already greatly restricted images, including but not
+		limited to NAND_SPL configurations.
+
 Low Level (hardware related) configuration options:
 ---------------------------------------------------