Pass struct vm_page_md * where possible.

This causes 1% code increase, mainly because additional argument
(paddr_t) affects register usage.  This will be fixed when per-page
data structure (struct vm_page) is redone, and physical address
can be retrieved from struct vm_page_md *.

Tested on (uncommitted) i.MX35 (ARM1136).

(uebayasi)