[PATCH 2/3] arm64: Make use of NUMBER(VA_BITS) in vmcoreinfo

Make use of the NUMBER(VA_BITS) in vmcoreinfo, which was added by
kernel commit 20a166243328 (Linux 4.12 and later kernels), as the
current way of guessing VA_BITS does not work on Linux 5.4 and
later kernels.

Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>
Signed-off-by: Kazuhito Hagio <k-hagio-ab@nec.com>