The GET EVENT STATUS NOTIFICATION is a mandatory command according
to MMC-3, even if event status notification is not supported.

This patch adds support for this command. It returns NEA ("No Event
Available") with an empty "Supported Event Classes" to show that it
doesn't event support status notification. If asychronous operation is
requested, which requires NCQ support, it returns an error according
to the specifications.

This fixes HAL support on FreeBSD and derivatives, which fill up the
logs every second with:

  acd0: FAILURE - unknown CMD (0x03) ILLEGAL REQUEST asc=0x20 ascq=0x00
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>