mtip32xx: updates based on feedback

* queue ncq commands when a non-ncq is in progress or error handling is active
* merge variables 'internal_cmd_in_progress' and 'eh_active' into new variable 'flags'
* get rid of read/write semaphore 'internal_sem'
* new service thread to issue queued commands
* use macros from ata.h for command codes
* return ENOTTY for BLKFLSBUF ioctl
* style changes

Signed-off-by: Asai Thambi S P <asamymuthupa@micron.com>
Signed-off-by: Sam Bradshaw <sbradshaw@micron.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>