arm64: defconfig: add MEDIA_PLATFORM_SUPPORT

Commit 06b93644

 ("media: Kconfig: add an option to filter in/out
platform drivers") adds a new Kconfig symbol which now hides drivers
currently enabled in the arm64 defconfig. Enable it to get those
drivers back.

Link: https://lore.kernel.org/r/20200427134003.45188-5-max.krummenacher@toradex.com
Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>