mtd, nand: Move common functions from cmd_nand.c to common place

Move common functions from cmd_nand.c (for calculating offset
and size from cmdline paramter) to common place, so they could
used from other commands which use mtd partitions.

For onenand the arg_off_size() is left in common/cmd_onenand.c.
It should use now the common arg_off() function, but as I could
not test onenand I let it there ...

Signed-off-by: Heiko Schocher <hs@denx.de>
Acked-by: Scott Wood <scottwood@freescale.com>
Reviewed-by: Jagannadh Teki <jteki@openedev.com>

lib/vsprintf.c

@@ -909,3 +909,19 @@ void print_grouped_ull(unsigned long long int_val, int digits)
 		grab = 3;
 	}
 }
+
+bool str2off(const char *p, loff_t *num)
+{
+	char *endptr;
+
+	*num = simple_strtoull(p, &endptr, 16);
+	return *p != '\0' && *endptr == '\0';
+}
+
+bool str2long(const char *p, ulong *num)
+{
+	char *endptr;
+
+	*num = simple_strtoul(p, &endptr, 16);
+	return *p != '\0' && *endptr == '\0';
+}