ANDROID: KVM: arm64: Add protected_hyp_mem VM statistic

When using nVHE in protected mode, the host allocates memory for the
hypervisor to store internal structures and the stage-2 page tables.
This has been proven to be an interesting value to follow, for debug and
health purpose. Account for those allocations in bytes, in a newly
created VM statistic "protected_hyp_mem".

Bug: 357781595
Bug: 278749606
Bug: 222044477
Change-Id: I18657d275f2ced67ceb6d0e4bd5ce41cf1d41dc8
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>