mips: octeon: octeon_ebb7304_defconfig: Fix CFI flash setup

This patch makes the necessary adjustments in the defconfig to fully
support the CFI flash on the Octeon EBB7304.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Aaron Williams <awilliams@marvell.com>
Cc: Chandrakala Chavva <cchavva@marvell.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>