Fix incorrect use of getenv() before relocation

Fix incorrect use of getenv() before relocation

A large number of boards incorrectly used getenv() in their board init
code running before relocation.  In some cases this caused U-Boot to
hang when certain environment variables grew too long.
Fix the code to use getenv_r().

Signed-off-by: Wolfgang Denk <[email protected]>
Cc: Stefan Roese <[email protected]>
Cc: The LEOX team <[email protected]>
Cc: Michael Schwingen <[email protected]>
Cc: Georg Schardt <[email protected]>
Cc: Werner Pfister <[email protected]>
Cc: Dirk Eibach <[email protected]>
Cc: Peter De Schrijver <[email protected]>
Cc: John Zhan <[email protected]>
Cc: Rishi Bhattacharya <[email protected]>
Cc: Peter Tyser <[email protected]>