vfs: Fase 2 - block device abstraction and refcount

vfs: Fase 2 - block device abstraction and refcount

- Modified init_mount_fs to accept block_device_t* instead of int drive
- Updated sys_mount, init.c, kconsole.c to use blockdev_find instead of ata_name_to_drive
- Registered virtio-blk as block_device_t (/dev/vda) with blockdev ops wrappers
- Updated fat_mount and ext2_mount to accept block_device_t*
- Added refcount field to block_device_t
- Implemented blockdev_claim and blockdev_release
- Added bdev field to vfs_mount struct
- Integrated blockdev_claim/release in init_mount_fs and vfs_umount_nolock
- Updated vfs_mount_full and vfs_mount_nolock_full signatures to accept bdev
- Added blockdev.h include to fs.h