arm64: defconfig: enable EFI_CAPSULE_LOADER

CONFIG_EFI_CAPSULE_LOADER allows the user to update the EFI firmware,
which is useful on ARM64 server platforms.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>