v2:
 - Actually applied the changes this time ...
 - And added a test to the AHCI suite...
 - ...Which revealed a few small issues in the suite.

The AHCI test should be sufficient in terms of general proof
for ATAPI regardless of the HBA used.

________________________________________________________________________________

For convenience, this branch is available at:
https://github.com/jnsnow/qemu.git branch ide-fix-read-cd
https://github.com/jnsnow/qemu/tree/ide-fix-read-cd

This version is tagged ide-fix-read-cd-v2:
https://github.com/jnsnow/qemu/releases/tag/ide-fix-read-cd-v2