Revert "kconfig: remove 'kvmconfig' and 'xenconfig' shorthands"

Revert "kconfig: remove 'kvmconfig' and 'xenconfig' shorthands"

This reverts commit 17a08680ab6a6c057949cb48c352933e09ea377a which is
commit 9bba03d4473df0b707224d4d2067b62d1e1e2a77 upstream.

Link: https://lore.kernel.org/r/20210119182837.GA18123@duo.ucw.cz
	I don't believe this is suitable for stable.

And he's right.  It is "after" 5.10.0, but we want to keep these targets
for all of the 5.10.y series.

Reported-by: Pavel Machek <pavel@ucw.cz>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>