powerpc: Rename is_kvm_guest() to check_kvm_guest()

We want to reuse the is_kvm_guest() name in a subsequent patch but
with a new body. Hence rename is_kvm_guest() to check_kvm_guest(). No
additional changes.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: kernel test robot <lkp@intel.com> # int -> bool fix
[mpe: Fold in fix from lkp to use true/false not 0/1]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201202050456.164005-3-srikar@linux.vnet.ibm.com