arm: dra7xx: Update the EXTRA_ENV_SETTINGS

Update the EXTRA_ENV_SETTING for the dra7xx.
The console needs to be set to ttyO0 and the
findfdt needs to be updated to load the
dra7xx-evm.dtb file.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
Reviewed-by: Tom Rini <trini@ti.com>