[lldb][Process/FreeBSDKernelCore] Set kernel displacement (#183975)

Use `kvm_kerndisp()` on core load to retrieve the kernel displacement,
that is the difference between the kernel's
base virtual address at run time and the kernel base virtual address
specified in the kernel image file. Currently PowerPC is the only
architecture supporting kernel displacement.

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Signed-off-by: Minsoo Choo <minsoochoo0122@proton.me>
GitOrigin-RevId: 62d06083ef186abe610de4742c62c84c2f97fcd0