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

This reverts commit 17a0868 which is
commit 9bba03d upstream.

As Pavel says at 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>

scripts/kconfig/Makefile

@@ -94,6 +94,16 @@ configfiles=$(wildcard $(srctree)/kernel/configs/$@ $(srctree)/arch/$(SRCARCH)/c
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/kconfig/merge_config.sh -m .config $(configfiles)
 	$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
 
+PHONY += kvmconfig
+kvmconfig: kvm_guest.config
+	@echo >&2 "WARNING: 'make $@' will be removed after Linux 5.10"
+	@echo >&2 "         Please use 'make $<' instead."
+
+PHONY += xenconfig
+xenconfig: xen.config
+	@echo >&2 "WARNING: 'make $@' will be removed after Linux 5.10"
+	@echo >&2 "         Please use 'make $<' instead."
+
 PHONY += tinyconfig
 tinyconfig:
 	$(Q)$(MAKE) -f $(srctree)/Makefile allnoconfig tiny.config