usr.bin: introduce dump2elf(1)

[minsoochoo0122_proton.me]

Summary

This program is a simple wrapper around kvm_convert_to_elf. It is used
to convert kernel crash dump to ELF core format.

Signed-off-by: Minsoo Choo <[e-mail]>
Sponsored by: The FreeBSD Foundation

Test Plan

With D56256, run

$ sudo LD_LIBRARY_PATH=/usr/obj/usr/src/freebsd/main/arm64.aarch64/lib/libkvm ./dump2elf -k /boot/kernel/kernel -c /var/crash/vmcore.last ~/vmcore.elf
# or
$ sudo LD_LIBRARY_PATH=/usr/obj/usr/src/freebsd/main/arm64.aarch64/lib/libkvm ./dump2elf -r -k /boot/kernel/kernel -c /var/crash/vmcore.last ~/vmcore.elf.raw

The result shows:

$ ls -lh /var/crash/vmcore.3
-rw-------  1 root wheel   13G Apr 15 03:17 /var/crash/vmcore.3

$ ls -lh vmcore.elf
-rw-r--r--  1 root minsoochoo  1.1G Apr 20 06:26 vmcore.elf

[minsoochoo0122_proton.me]

Use kvm_openfiles() instead

[minsoochoo0122_proton.me]

Since D56250 has changed to accomodate full dumps as well, rename this utility to dump2elf and update code and man page accordingly.

[minsoochoo0122_proton.me]

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[minsoochoo0122_proton.me]

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