KVM: selftests: Use gpa_t instead of vm_paddr_t

KVM: selftests: Use gpa_t instead of vm_paddr_t

Replace all occurrences of vm_paddr_t with gpa_t to align with KVM code
and with the conversion helpers (e.g. addr_hva2gpa()).

This commit was generated with the following command:

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

Then by manually adjusting whitespace to make checkpatch.pl happy.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@google.com>
[sean: drop bogus changelog blurb about renaming functions]
Link: https://patch.msgid.link/20260420212004.3938325-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>