[PATCH] libata: use preallocated buffers

It's not a very good idea to allocate memory during EH.  Use
statically allocated buffer for dev->id[] and add 512byte buffer
ap->sector_buf.  This buffer is owned by EH (or probing) and to be
used as temporary buffer for various purposes (IDENTIFY, NCQ log page
10h, PM GSCR block).

Signed-off-by: Tejun Heo <htejun@gmail.com>