virtio issues

Build virtio-* and ext* filesystem driver in kernel, not as module.

PS: this patch also removes many drivers which are not used by KVM machine

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
update kernel version to linus's git 61f98

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>