powerpc/ppc4xx: Remove CONFIG_SYS_FLASH_PROTECTION from gdsys boards

CONFIG_SYS_FLASH_PROTECTION was active on most gdsys boards by default,
while hardware flash protection was not implemented.
Hardware support was added recently and we get into trouble because backward
compatibility is broken (u-boot can't unprotect the protected flash after a
downgrade). So we decided to disable hardware flash protection for all our boards.

Signed-off-by: Dirk Eibach <dirk.eibach@gdsys.cc>
Signed-off-by: Stefan Roese <sr@denx.de>