Replaced osi_getbuf()/osi_freebuf() with osi_malloc()/osi_free()

Removed the alternative buffer allocation osi_getbuf() / osi_freebuf()
and use instead osi_malloc() / osi_free().

Correspondingly, replaced usage of osi_freebuf_and_reset()
with osi_free_and_reset().

Bug: 24914560
Change-Id: I7a9599ba7fa900321f087da684428133eb0ddd6b