init: move initial property area allocation into bionic

bionic's __system_property_add() now expands the property area as needed
by mapping in more pages.  Rather than duplicate the mapping code, move
it inside bionic and have bionic's __system_property_area_init() set up
the first page.

Change-Id: If9917d5f775c1a82eb89be55b84635395145ca49
Signed-off-by: Greg Hackmann <ghackmann@google.com>