virtio: console: Replace deprecated kmap_atomic with kmap_local_page

kmap_atomic() is deprecated and should be replaced with kmap_local_page()
[1][2]. kmap_local_page() is faster in kernels with HIGHMEM enabled, can
take page faults, and allows preemption.

According to [2], this replacement is safe as long as the code between
kmap_atomic() and kunmap_atomic() does not implicitly depend on disabling
page faults or preemption. In this patch, the only thing happening between
mapping and unmapping the page is a memcpy, and I don't suspect it depends
on disabling page faults or preemption.

[1] https://lwn.net/Articles/836144/
[2] https://docs.kernel.org/mm/highmem.html#temporary-virtual-mappings

Signed-off-by: David Reaver <me@davidreaver.com>
Reviewed-by: Amit Shah <amit@kernel.org>
Link: https://lore.kernel.org/r/20250109035904.168345-1-me@davidreaver.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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