Revert "media: subdev: disallow ioctl for saa6588/davinci"

This reverts commit 917791e4.

It breaks the ABI and isn't needed for android devices at this point in
time.

Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ief4824f92133b6749e479cd0e9aa8d9fe330b8c2