entry: KVM: Allow use of generic KVM entry w/o full generic support

Some architectures (e.g. arm64) have yet to adopt the generic entry
infrastructure. Despite that, it would be nice to use some common
plumbing for guest entry/exit handling. For example, KVM/arm64 currently
does not handle TIF_NOTIFY_PENDING correctly.

Allow use of only the generic KVM entry code by tightening up the
include list. No functional change intended.

Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210802192809.1851010-3-oupton@google.com