libparted: avoid the HDIO_GETGEO ioctl when possible

libparted: avoid the HDIO_GETGEO ioctl when possible

We were using the long depreciated HDIO_GETGEO ioctl on the
partition to get its start sector.  Use the new BLKPG_GET_PARTITION
ioctl instead.  This allows for disks > 2TB and partitioned loop
devices, which don't support HDIO_GETGEO.  As a fallback when
BLKPG_GET_PARTITION fails or is not availible, try getting the
values from sysfs, and finally use BLKGETSIZE64 and HDIO_GETGEO
as a last resort.