UBI: Add basic UBI support to U-Boot (Part 6/8)

This patch adds basic UBI (Unsorted Block Image) support to U-Boot.
It's based on the Linux UBI version and basically has a "OS"
translation wrapper that defines most Linux specific calls
(spin_lock() etc.) into no-ops. Some source code parts have been
uncommented by "#ifdef UBI_LINUX". This makes it easier to compare
this version with the Linux version and simplifies future UBI
ports/bug-fixes from the Linux version.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Stefan Roese <sr@denx.de>

include/exports.h

@@ -25,6 +25,7 @@ char *getenv (char *name);
 int setenv (char *varname, char *varvalue);
 long simple_strtol(const char *cp,char **endp,unsigned int base);
 int strcmp(const char * cs,const char * ct);
+int ustrtoul(const char *cp, char **endp, unsigned int base);
 #ifdef CONFIG_HAS_UID
 void forceenv (char *varname, char *varvalue);
 #endif