KVM: selftests: Use gva_t instead of vm_vaddr_t

KVM: selftests: Use gva_t instead of vm_vaddr_t

Replace all occurrences of vm_vaddr_t with gva_t to align with KVM code
and with the conversion helpers (e.g. addr_gva2hva()).

This commit was generated with the following command:

  git ls-files tools/testing/selftests/kvm | xargs sed -i 's/vm_vaddr_/gva_/g'

Then by manually adjusting whitespace to make checkpatch.pl happy, and
dropping renames of functions that allocate memory within a given VM.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@google.com>
[sean: drop renames of allocator APIs]
Link: https://patch.msgid.link/20260420212004.3938325-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>