Add GetBlockDevSize, GetBlockDevSectors helpers

Helpers to get a block device size in bytes or 512 byte sectors,
using BLKGETSIZE64 and returning value of uint64_t type.

This also removes get_blkdev_size().

Test: build, manual, mount exFAT volume
Bug: 80202067
Change-Id: Ib07e8ac6ef7ff49de0ed570d1fa202e8b558b80c
8 files changed