arm64: Create a TLBI invalidate for the kernel

Add pmap_s1_invalidate_all_kernel to remove the need to check for the
kernel_pmap when it's passed in.

While here replace pmap calls to cpu_tlb_flushID with
pmap_s1_invalidate_all_kernel as they are identical.

Reviewed by: kib
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D52183