x86, kvm: Fix intialization warnings in kvm.c

With commit:

  4cca6ea0 ("x86/apic: Allow x2apic without IR on VMware platform")

we started seeing "incompatible initialization" warning messages,
since x2apic_available() expects a bool return type while
kvm_para_available() returns an int.

Reported by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Alok N Kataria <akataria@vmware.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>