stingray: Fix board configuration typo.
stingray: Fix board configuration typo.

Default board configuration was set to bcm958742k which is not present
in current codebase. This causes a default platform build to fail.
Changing to bcm958742t.

Signed-off-by: Max Shvetsov <554ef60c0309fcb96f307a2e251c72d0c11c8b0b@arm.com>
Change-Id: Ie24f94ef0ef316ff56fe142df5de45d70ba93c28

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware