mmc: sdhci-of-aspeed: test: Use kunit_test_suite() macro

The kunit_test_suite() macro is no-longer incompatible with module_add,
so its use can be reinstated.

Since this fixes parsing with builtins and kunit_tool, also enable the
test by default when KUNIT_ALL_TESTS is enabled.

The test can now be run via kunit_tool with:
	./tools/testing/kunit/kunit.py run --arch=x86_64 \
	--kconfig_add CONFIG_OF=y --kconfig_add CONFIG_OF_ADDRESS=y \
	--kconfig_add CONFIG_MMC=y --kconfig_add CONFIG_MMC_SDHCI=y \
	--kconfig_add CONFIG_MMC_SDHCI_PLTFM=y \
	--kconfig_add CONFIG_MMC_SDHCI_OF_ASPEED=y \
	'sdhci-of-aspeed'

(It may be worth adding a .kunitconfig at some point, as there are
enough dependencies to make that command scarily long.)

Acked-by: Daniel Latypov <dlatypov@google.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>