Move uvm_pmr_zero_everything() to subr_hibernate.

This function will probably die before ever being called
from the in-tree code, since hibernate will move to RLE encoding.

No functional change, fu

Move uvm_pmr_zero_everything() to subr_hibernate.

This function will probably die before ever being called
from the in-tree code, since hibernate will move to RLE encoding.

No functional change, function had no callers.

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Move hiballoc to hibernate.h, subr_hibernate.c
Next few commits will move other hibernate-specific functionality,
like the pig-allocator, to subr_hibernate.

No functional change, no callers either.