Custom SMART display options

[Krzaku]

This is primarily useful for Seagate drives which sometimes use the lower 32 bits of the SMART value to indicate the total number of events that could lead to an error (eg. total number of reads etc.), and the upper 16 bits to store the actual error value. This is already supported by smartctl, but needs to be configured using the "-v" option. The way you use this option is by setting which octets of a value are actually read, and so, setting it to "-v 1,raw48:543210" would read the whole 48 bits, but setting it to "-v 1,raw48:54" would only read the upper 16 bits, which is the error value we want. My request is to implement support for this "-v" option on the SMART display screen, so we can get actually useful SMART error notifications for these drives.