ide-tape: remove struct idetape_capabilities_page_t

All those 2-byte values denoting the different capabilities are being written to
the local copy of the caps buffer without being converted to big endian for
simplicity of usage and shorter code later.  Also, we add some comments stating
which are the fields of the caps page in question in order to alleviate the
cryptic pointer casting exercises as in e.g. idetape_get_mode_sense_results().

There should be no functional changes resulting from this patch.

Bart:
- remove two needless "!!"
Signed-off-by: Borislav Petkov <bbpetkov@yahoo.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>