configs/raspberrypi3_defconfig: increase filesystem size

configs/raspberrypi3_defconfig: increase filesystem size

Increase the filesystem size for raspberrypi3 by setting
BR2_TARGET_ROOTFS_EXT2_SIZE to "120M". The filesystem for
raspberrypi3_64 has the same size. The size is so large because the
kernel config enables many many modules.

Fixes:
Copying files into the device: __populate_fs: Could not allocate block in ext2 filesystem while writing file "services"
mkfs.ext4: Could not allocate block in ext2 filesystem while populating file system

This error is not reproducible, it seems to depend on e.g. directory
ordering.

Signed-off-by: Leon Anavi <leon.anavi@konsulko.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>