Can't use disklabel to find the real size of a disk since a fake disklabel
read from disk is trusted. Revert to use drvctl again.

Handle arbitrary raw partitions.
Fetch geometry from disklabel to be consistent.
Use disktab format instead of the normal human-readable output for parsing
the disklabel.
Avoid overflows in size comp

Handle arbitrary raw partitions.
Fetch geometry from disklabel to be consistent.
Use disktab format instead of the normal human-readable output for parsing
the disklabel.
Avoid overflows in size computation.

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resize_disklabel: if disk and partition is not specified, use kern.root_device/kern.root_partition sysctls

Grow the MBR partition table entry for the BSD partition before
growing the disklabel.

Add support for auto-growing the root partition. Enable it for rpi.img.