vsprintf.c: Always enable CONFIG_SYS_VSNPRINTF

Enabling this function always removes some class of string saftey issues.
The size change here in general is about 400 bytes and this seems a reasonable
trade-off.

Cc: Peng Fan <peng.fan@nxp.com>
Cc: Peter Robinson <pbrobinson@gmail.com>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Adrian Alonso <aalonso@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Tom Rini <trini@konsulko.com>

README

@@ -890,15 +890,6 @@ The following options need to be configured:
 		'Sane' compilers will generate smaller code if
 		CONFIG_PRE_CON_BUF_SZ is a power of 2
 
-- Safe printf() functions
-		Define CONFIG_SYS_VSNPRINTF to compile in safe versions of
-		the printf() functions. These are defined in
-		include/vsprintf.h and include snprintf(), vsnprintf() and
-		so on. Code size increase is approximately 300-500 bytes.
-		If this option is not given then these functions will
-		silently discard their buffer size argument - this means
-		you are not getting any overflow checking in this case.
-
 - Boot Delay:	CONFIG_BOOTDELAY - in seconds
 		Delay before automatically booting the default image;
 		set to -1 to disable autoboot.