config/ast2600: Disable hash hardware accel

config/ast2600: Disable hash hardware accel

The HACE driver lacks support for all the hash types, causing boot to
fail with the default FIT configuration which uses CRC32.

Additionally the Qemu model or the u-boot driver is unable to correctly
compute the SHA256 hash used in a FIT.

Disable HACE by default while the above issues are worked out to enable
boot testing in Qemu.

Reviewed-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>