KVM: selftests: Use gpa_t for GPAs in Hyper-V selftests

KVM: selftests: Use gpa_t for GPAs in Hyper-V selftests

Fix various Hyper-V selftests to use gpa_t for variables that contain
guest physical addresses, rather than gva_t.  In practice, the bugs are
benign as both gva_t and gpa_t are u64 typedefs, i.e. gpa_t and gva_t are
interchangeable from a functional perspective, the code is just confusing.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@google.com>
[sean: call out that both are u64 typedefs]
Link: https://patch.msgid.link/20260420212004.3938325-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>