virt: sevguest: Rename the sevguest dir and files to sev-guest

Rename the drivers/virt/coco/sevguest directory and files to sev-guest
so as to match the driver name.

  [ bp: Rename Documentation/virt/coco/sevguest.rst too, as reported by sfr:
    https://lore.kernel.org/r/20220427101059.3bf55262@canb.auug.org.au

 ]

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/2f5c9cb16e3a67599c8e3170f6c72c8712c47d53.1650464054.git.thomas.lendacky@amd.com