KVM: selftests: Add option to create 2M and 1G EPT mappings

The current EPT mapping code in the selftests only supports mapping 4K
pages. This commit extends that support with an option to map at 2M or
1G. This will be used in a future commit to create large page mappings
to test eager page splitting.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220520233249.3776001-3-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>