KVM: arm64: Make __pkvm_create_mappings static

The __pkvm_create_mappings() function is no longer used outside of
nvhe/mm.c, make it static.

Signed-off-by: Quentin Perret <qperret@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210809152448.1810400-22-qperret@google.com