SCSI id 7 is unusable/hardcoded

[iflyhigh]

According to https://github.com/erichelgeson/BlueSCSI/wiki/Usage , one can use up to 7 images on one SD, thus reserving one ID for SCSI controller. But current implementation assumes that ID 7 is used as controller ID:

if(id < NUM_SCSIID && lun < NUM_SCSILUN) { dev = &scsi_device_list[id][lun]; ...
Since NUM_SCSIID == MAX_SCSIID == 7, only IDs below 7 (i.e., 0-6) are processed as images' IDs. Some Akai samplers by default use ID 6 as internal one which limits total number of possible images to 6 on these platforms. Although these samplers support changing their ID even on the fly, default ROM image which is always booted first during system startup (actual OS with another configured ID can be booted later from FDD or HDD), has hardcoded value of 6. Having both sampler ID set to 6 and a BlueSCSI device with ID 6 during boot time causes some weird issues on a sampler unless internal ID is manually changed even in case the OS booted later has another ID set as internal.

[erichelgeson]

Once we merge in the ini config file support we can likely make the reserved ID configurable.