Pull up following revision(s) (requested by skrll in ticket #671):

sys/uvm/pmap/pmap.c: revision 1.78
sys/uvm/pmap/pmap.h: revision 1.27

Fix types in pmap_page_clear_attributes so that the top bits of
the u_long mdpg_attrs aren't dropped giving atomic_cas_ulong no
chance of completing if any of the top bits is set.

Update pmap_page_set_attributes for consistency.

An ATF test run completed for me with this fix.

port-riscv/58006: ATF tests no longer complete on riscv-riscv64

(martin)