[Blackfin] arch: move the init sections to the end of memory

Move the init sections to the end of memory so that after they
are free, run time memory is all continugous - this should help decrease
memory fragementation.

When doing this, we also pack some of the other sections a little closer
together, to make sure we don't waste memory. To make this happen,
we need to rename the .data.init_task section to .init_task.data, so
it doesn't get picked up by the linker script glob.

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>