Rename getenv_r() into getenv_f()

While running from flash, i. e. before relocation, we have only a
limited C runtime environment without writable data segment. In this
phase, some configurations (for example with environment in EEPROM)
must not use the normal getenv(), but a special function.  This
function had been called getenv_r(), with the idea that the "_r"
suffix would mean the same as in the _r_eentrant versions of some of
the C library functions (for example getdate vs. getdate_r, getgrent
vs. getgrent_r, etc.).

Unfortunately this was a misleading name, as in U-Boot the "_r"
generally means "running from RAM", i. e. _after_ relocation.

To avoid confusion, rename into getenv_f() [as "running from flash"]

Signed-off-by: Wolfgang Denk <wd@denx.de>
Acked-by: Detlev Zundel <dzu@denx.de>

post/post.c

@@ -187,7 +187,7 @@ static void post_get_flags (int *test_flags)
 	}
 
 	for (i = 0; i < varnum; i++) {
-		if (getenv_r (var[i], list, sizeof (list)) <= 0)
+		if (getenv_f(var[i], list, sizeof (list)) <= 0)
 			continue;
 
 		for (j = 0; j < post_list_size; j++) {