boards: remove the no longer used CONFIG_EHCI_DCACHE

CONFIG_EHCI_DCACHE was removed by commit b8adb120
"USB: Drop cache flush bloat in EHCI-HCD". Remove the defines from
the boards configs as well.

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
cc: Marek Vasut <marex@denx.de>
cc: Stefan Roese <sr@denx.de>
cc: Tom Rini <trini@ti.com>
cc: Wolfgang Denk <wd@denx.de>
cc: Thierry Reding <thierry.reding@avionic-design.de>
cc: Tom Warren <twarren@nvidia.com>
cc: Stephen Warren <swarren@nvidia.com>
cc: Stefano Babic <sbabic@denx.de>