block: genhd: Add disk/partition specific uevent callbacks for partition info

block: genhd: Add disk/partition specific uevent callbacks for partition info

For disk devices, a new uevent parameter 'NPARTS' specifies the number
of partitions detected by the kernel. Partition devices get 'PARTN' which
specifies the partitions index in the table, and 'PARTNAME', which
specifies PARTNAME specifices the partition name of a partition device

Signed-off-by: Dima Zavin <dima@android.com>
(cherry picked from commit 9b9ae694cce47e568fd8f7619c70f1fc91e5b81d)

Change-Id: I5cb7496c9dcd7659116f1b4d5577ac85be102fb5