arm64: include VIRTIO_{MMIO,BLK} in defconfig

Currently, development on arm64 is aided by a Foundation_v8 emulator
distributed by ARM [1]. To run their kernels, users will execute:

  $ ./Foundation_v8 --image linux-system.axf --block-device raring-rootfs

To mount the raring-rootfs filesystem, the kernel parameter should
typically include:

  root=/dev/vda

For this device to be present, the kernel must be compiled with
VIRTIO_{MMIO,BLK}. To make this work out-of-the-box, make it part of the
default configuration.

[1]: https://silver.arm.com/browse/FM00A

Cc: Will Deacon <will.deacon@arm.com>
Cc: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/configs/defconfig

@@ -42,7 +42,7 @@ CONFIG_IP_PNP_BOOTP=y
 # CONFIG_WIRELESS is not set
 CONFIG_UEVENT_HELPER_PATH="/sbin/hotplug"
 CONFIG_DEVTMPFS=y
-# CONFIG_BLK_DEV is not set
+CONFIG_BLK_DEV=y
 CONFIG_SCSI=y
 # CONFIG_SCSI_PROC_FS is not set
 CONFIG_BLK_DEV_SD=y
@@ -91,3 +91,5 @@ CONFIG_DEBUG_KERNEL=y
 CONFIG_DEBUG_INFO=y
 # CONFIG_FTRACE is not set
 CONFIG_ATOMIC64_SELFTEST=y
+CONFIG_VIRTIO_MMIO=y
+CONFIG_VIRTIO_BLK=y