kvm: initialize qemu_host_page_size

There is a HOST_PAGE_ALIGN macro which makes sense for KVM accelerator
but it uses qemu_host_page_size/qemu_host_page_mask which initialized
for TCG only.

This moves qemu_host_page_size/qemu_host_page_mask initialization from
TCG's page_init() and adds a call for it from kvm_init().

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
