kexec: rename 'virt' to 'userspace'
kexec: rename 'virt' to 'userspace'

virt can be confusing in the context of ELF or PE images, where
sections' target/load addresses can be called "virtual addresses". In
kexec, the load address of a section is in the physical address space
(if paging enabled, it must is 1:1-mapped).

Signed-off-by: Chris Koch <cd2178739c1fb8f241acc6c7bd5abe02c150d7e5@google.com>

u-root/u-root,u-root/u-root,u-root/u-root