ARM: ep93xx: enable all boards in the EP93xx defconfig

With PATCH_PHYS_TO_VIRT we can support all EP93xx variants
in a single image, so enable all board variants in the defconfig
for simplicity and build coverage.

Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>