igep00x0: disable environment

ISEE's U-Boot and Linux are using 1bit ECC scheme, while we
switched to 8bit ECC to fullfill flash specification requirements.
However when trying to run U-Boot on board with 1bit ECC'd data
on flash, UBI code takes several minutes to pass scan as reading
of every block ends with ecc error (which is also printed on
console).
So, until proper solution is developed, disable environment
alltogether.

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>