Fill in missing parts of the ATAPI/CAM XPT: implement XPT_RESET_BUS

Fill in missing parts of the ATAPI/CAM XPT: implement XPT_RESET_BUS
and XPT_RESET_DEV.

In order to properly handle reset requests whether they originate in the
ATA layer (atacontrol reinit) or from the CAM layer (camcontrol reset)
ata_reinit does not cause the SIM to be deallocated anymore. The SIM
is now unconditionnally created for each ATAPI bus.

This change may cause existing bus ids to change on some setups.

Reviewed by:	roberto
Approved by:	sos