Make flash protection work, when the environment is in EEPROM

On the pcm030 the environment is located in the onboard EEPROM. But we want
to handle flash sector protection in a safe manner. So we must read the
unlock environment variable from EEPROM instead from flash.

This patch is required as long the evironment is saved into the EEPROM.

Stefan: Additional change as suggested by Wolfgang, use bigger char array
(instead of 4).

Signed-off-by: Eric Schumann <E.Schumann@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>