Add PC_FLAG_DRQ_INTERRUPT pc flag, set it in ide*_do_request()
and check for it (instead of checking for IDE*_FLAG_DRQ_INTERRUPT)
in ide*_issue_pc().  This is a preparation for adding generic
ide_issue_pc() helper.

There should be no functional changes caused by this patch.

Cc: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>