Eliminate the remaining TODOs in hw/ide/piix.c by:
* Using pci_set_{size} functions to write the PIIX PCI configuration
  space instead of manipulating it directly as an array; and
* Documenting the default register values by reference to the
  controlling specification.

Signed-off-by: Lev Kujawski <lkujaw@member.fsf.org>
Message-Id: <20220707031140.158958-1-lkujaw@member.fsf.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>