platform/arm64: build drivers even on non-ARM64 platforms

platform/arm64: build drivers even on non-ARM64 platforms

The Kconfig for platforms/arm64 has 'depends on ARM64 || COMPILE_TEST'.
However due to Makefile having just obj-$(CONFIG_ARM64) the subdir will
not be descended for !ARM64 platforms and thus the drivers won't get
built. This breaks modular builds of other driver drivers which depend
on arm64 platform drivers.

Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Fixes: 363c8aea2572 ("platform: Add ARM64 platform directory")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20240624-ucsi-yoga-ec-driver-v9-1-53af411a9bd6@linaro.org
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>