ion: support creation of mm heap in a fixed place

The multimedia firmware on 8960 will always be
loaded into a fixed address, and all callers into
this firmware must be no more than 256M above the
start of this firmware.

This implies that the the mm ION heap and its associated heaps
(mm_fw and mfc) must also be created in a fixed place.

This version of the patch keeps the mm fw heap size
to 2M for compatibility with the current tip. This
will eventually be reduced to 1M.

Change-Id: I35f89b8c60165fb0adbb9d04412e0e200117beb9
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
[sboyd: drop memory.c changes]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>